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AUDELS 

ENGINEERS 

ANO 

MECHANICS 
GUIDE  1 

/\  PR06RESSIVF.  ILLUSTRATED  SERIES 
WITH  QUESTIONS-ANSWERS 
CALCULATIONS 

covEaiNG 

MODERN 
ENGINEERING  PRACTICE 

SPECIALLY  PREPARED  FOR  ALL  ENGINEERS 
ALL  MECHANICS  AND  ALL  ELECTRICIANS. 
A  PRACTICAL  COURSE  OF  STUDY  AND 
REFERENCE  FOR  ALL  STUDENTS  AND 
WORKERS  IN  EVERY  BRANCH  OF  THE 
ENGINEERING  PROFESSION 
BY 

FRANK  D.  GRAHAM, BS.,M.S.,M.E. 

GRADUATE  PRINCETON  UNIVERSITY 
AND  STEVENS  INSTITUTE-LICENSED 
STATIONARY  AND  MARINE  ENGINEER 


THEO.  AUDEL    8c  CO.  .       pubushers 
72  FIFTH  AVE.      NEW  YORK       u.s.a. 


COPYRIGHTED,  1921, 

BY 

THEO.  AUDEL  &  CO., 
New  York 


■tted  in  the  United  States 


NOTE 


In  planning  this  helpful  series  of  Educators,  it  has  been  the 
aim  of  the  author  and  publishers  to  present  step  by  step  a 
logical  plan  of  study  in  General  Engineering  Practice,  taking 
the  middle  ground  in  making  the  information  readily  available  and 
showing  by  text,  illustration,  question  and  answer,  and  calcula- 
tion, the  theories,  fundamentals  and  modern  applications,  includ- 
ing construction  in  an  interesting  and  easily  understandable 
form. 

Where  the  question  and  answer  form  is  used,  the  plan  has 
been  to  give  shorty  simple  and  direct  answers,  limited  to  one 
paragraph,  thus  simplifying  the  more  complex  matter. 

In  order  to  have  ajiequate  space  for  the  presentation  of  the 
important  matter  and  not  to  divert  the  attention  of  the  reader, 
descriptions  of  machines  have  been  excluded  from  the  main 
text,  being  printed  in  smaller  type  under  the  illustrations. 

Leonardo  Da  Vinci  once  said: 

"Those  who  give  themselves  to  ready  and  rapid  practice 
before  they  have  learned  the  theor}^,  resemble  sailors  who  go 
to  sea  in  a  vessel  without  a  rudder" 

—in  other  words,  **a  little  knowledge  is  a  dangerous  thing.'** 
Accordingly  the  author  has  endeavored  to  give  as  much  infor- 
ination  as  possible  in  the  space  allotted  to  each  subject. 

The  author  is  indebted  to  the  various  manufacturers  for 
their  co-operation  in  furnishing  cuts  and  information  relat- 
ing to  their  products. 

These  books  will  speak  for  themselves  and  will  find  their 
place  in  the  great  field  of  Engineering. 


CONTENTS  OF  GUIDE  No.  1 


Contents  of  Guide  No.  1 

CHAPTER  PAGES        \ 

1.  Basic  Principles 1  to  46  ] 

Water — heat — work — Joule^s    experiment — energy — pressure — the   bar-  - 
ometer — temperature  scales — steam — what  an   engineer  should   know 
about  steam — From  Ice  to  Steam — condensation— STEAM  TABLES,  i 

2.  The  Steam  Engine 47  to  102  | 

How  an  engine  works — expansion  of  steam — Boyle's  law — saving  by  '] 
expansion — cut  off — initial,  terminal  and  mean  elective  pressures —  ! 
hypobolic  logarithms — diagram  factor — horse  power — size  of  cylinder  j 
(calculations).  .  '     .  i 

3.  Steam  Engine  Parts 103  to  178 

Cylinder — stuffing  box — piston — piston  rod — cross  head  and  guides — 
Scotch  yoke — connecting  rod — crank  shaft — main  bearings — fly  wheel 
—belts. 

4.  Tlie  Slide  Valve ..,  179  to  224  I 

Requirements — valve — seat — steam  and  exhaust  edges — port — passage  j 
— wire  drawing — lap — neutral  and  line  and  line  positions — lead — pre-  | 
admission — admission — cut  off — pre-release — release — compression —  .■ 
port  opening — travel  (throw) — ^linear  advance — how  to  design  a  slide  I 
valve  for  a  7  X  7  engine  applying  the  Bilgram  diagram — defects  of  j 
the  slide  valve.  i 

i 

5.  The  Valve  Gear 225  to  242  1 

i 

Yoke — stem^-guide — rocker  levers — eccentric  rod — eccentric  and  strap  : 
— throw — angular  advance — objections  to  eccentrics .  \ 


CONTENTS  OF  GUIDE  No.  1 


6.  Variable  Cut  Off 243  to  290 

Principles  of  variable  cut  off — shifting,  swinging  and  offset  swinging 
eccentrics — independent  cut  o/f— defects  of  slide  valve  at  early  cut 
off — Gonzenback   valve — riding  cut   off,  with:   1,  variable   angular 
^K    advance;  2,  variable  lap;  3,  variable  travel. 

7'  Modified  Slide  Valves, . , 291  to  308 

Balanced  slide  valves — piston  valves — outside  and  inside  admission — 
double  admission — double  ports — compound  engine  valves — adjustable 
valve — pressure  plate  valves — quadruple  admission  and  double  exhaust 
— ball  valve. 

8.  Reversing   Valve    Gears;   Loose   Ec- 
centrics  e .  .  . .  309  to  316 

Principle  of  loose  eccentric — spiral  slot  marine  type:  1,  on  main  shaft; 
2,  on  valve  shaft — loose  eccentric  control  methods — various  drives  for 
loose  eccentrics — Rabbe  triple  expansion  marine  engine  illustrating 
adaptation  of  loose  eccentrics  to  marine  practice. 

9.  Reversing   Valve    Gears;    Link    Mo- 
tions  317  to  338 

Williams  link — so  called  Stephenson  or  shifting  link — single  and  double 
reach  rods — end  and  center  suspension — offset  link — open  and  crossed 
rods — adjustable  cut  off  with  shifting  link — forms  of  link — steam  dis- 
tribution with  link — slip — Gooch  link — stationary — Allen  and  Fink 
links. 

10.  Reversing  Valve  Gears;  Radial  Valve 
Motions 339  to  362 

Principles — Hackworth  gear:  1,  inside  connected;  2,  outside  connected 
types — Marshall  gear — Bremme  gear — ^Joy  gear— Joy  and  Bremme  gear 
compared — ^Walschaerts  gear. 

11.  Governors 363  to  402 

Classes   of   governor — centrifugal,    pendulum    and    loaded    pendulum 


CONTENTS  OF  GUIDE  No.  1 


Governors — Continued 

governors  —  sensitiveness  —  stability  —  isochronism  —  hunting  —  iner- 
tia governors — spring  governors — regulating  mechanism — throttling  and 
cut  off  governors — regulation — shaft  governors — auxiliary  devices — ^vari- 
able speed  governors— GOVERNOR  TROUBLES. 

12.  Pump  Valve  Gears ^. . .  403  to  432 

Principles — main  valve — auxiliary  piston — auxiliary  valve — separate 
auxiliary  valve — auxiliary  valve  and.  auxiliary  piston  combined — duplex 
valve  gear — method  of  locating  cross  head  centers — duplex  valve  setting; 
short  rules. 

13.  Valve  Setting 433  to  462 

How  to  set  the  slide  valve:  \,  finding  dead  center;  2,  adjusting  valve 
stem,  Z,  finding  angular  advance Xgeneial,  and  on  large  engines) — settmg 
slide  valve:  1,  without  removing  chest  cover;  2,  without  finding  dead 
centers;  3,  with  inside  admission;  4,  emergency  rule — taking  laths — 
setting  riding  cut  off  gear:  1,  movable  eccentric;  2,  fixed 'eccentric — setting 
link  motion — ^valve  setting  with  indicator. 


BASIC  PRINCIPLES 


CHAPTER  1 
BASIC  PRINCIPLES 


"'he  Medium. — In  the  operation  of  a  steam  engine,  steam 
is  the  medium  or  working  substance  by  which  some  of  the  heat 
energy,  liberated  from  the  fuel  by  combustiony  is  transmitted  to  the 
engine,  and  partly  converted  by  the  latter  into  mechanical  work. 
The  behavior  of  this  medium  under  various  conditions  should 
therefore  be  thoroughly  understood  by  the  engineer.  Accord- 
ingly, water,  from  which  it  is  formed  by  the  application  of  heat, 
should  be  first  considered. 

Water. — This  remarkable  substance  is  a  compound  of  hydrogen 
and  oxygen  in  the  proportion  of  2  parts  by  weight  of  hydrogen  to 
16  parts  by  weight  of  oxygen: 

Since  the  atom  of  oxygen  is  believed  to  weigh  16  times  as  much  as  the 
atom  of  hydrogen,  the  molecule  of  water  is  said  to  contain  2  atoms  of 
hydrogen  and  1  atom  of  oxygen,  being  represented  by  the  formula  H2O. 

Under  the  influence  of  temperature  and  pressure  this  substance  H2O 
may  exist  as 

1.  A  soHd; 

2.  A  liquid,  or 

3.  A  gas. 

As  a  solid  it  is  called  ice*\   as  a  liquid,  water,  and  as  a  gas,  steam. 


*NOTE. — One  cu.  ft.  of  ice  at  32"  Fahr.,  weighs  57.5  lbs.;  one  lb.  of  ice  at  32*  F.  has  a 
volume  of  .0174  cu.  ft.,  or  30.067  cu.  ins.  The  relative  volume  of  ice  to  water  at  32**  F.,  is 
1.0855,  the  expansion  in  passing  into  the  solid  state  being  8.55%.  Specific  gravity  of  ice  =.922, 
water  at  62°  F.  being  \.— Clark. 


BASIC  PRINCIPLES 


Oues.  What  is  the  most  remarkable  characteristic 
of  water? 

Ans.  Water  at  its  maximum  density  (39.1  degrees  F.)  will 
expand  as  heat  is  added,  and  it  will  also  expand  slightly  as  the 
temperature  falls  from  this  point,  as  illustrated  in  figs.  1  to  3. 

Ques.  What  is  the  freezing  and  boiling  points  of  water 
at  atmospheric  pressure  at  the  sea  level? 


MAXIMUM 
DENSITY 

Figs.  1  to  3. — The  most  remarkable  characteristic  of  water:  expansion  below  and  above  its 
temperature  or  "point  of  maximum  density"  39.1°Fahr.  Imagine  one  pound  of  water  at  39.1"  F. 
placed  in  a  cylinder  having  a  cross  sectional  area  of  1  sq.  in.  as  in  fig.  1.  The  water  having  a 
volume  of  27.68  cu.  ins.,  will  fill  the  cylinder  to  a  height  of  27.68  ins.  If  the  liquid  be  cooled 
it  will  expand,  and  at  say  the  freezing  point  32°  F.,  will  rise  in  the  tube  to  a  height  of  27.7  ins., 
as  in  fig.  2,  before  freezing.  Again,  if  the  liquid  in  fig.  1  be  heated,  it  will  also  expand  and 
rise  in  the  tube,  and  at  say  the  boiling  point  (for  atmospheric  pressure  212°  F.),  will  occupy 
the  tube  to  a  height  of  28.88  cu.  ins,  as  in  fig.  3. 


Ans.     It  will  freeze  at  32°  Fahr.,  and  boil  at  212°,  when  the 
barometer  reads  29.921  inches.* 

Oues.     Is  the  boiling  point  the  same  in  all  places? 

Ans.     No. 

The  boiling  point  of  water  will  lower  as  the  altitude  increases ;  at  an  alti- 
tude of  5,ooo  feet,  water  will  boil  at  a  temperature  of  202°  Fahr. 


*NOTE — 29.921  inches  of  mercury  =  standard  atmosphere=  14. ( 
Marks  and  Davis. 


>  lbs.  per  sq.  inch. — 


BASIC  PRINCIPLES 


Oues.     How  does  pressure  affect  the  boiling  point  of 
water?  \ 

Ans.     An  increase  of  pressure  will  elevate  the  boiling  point.     ■] 


Fig.  4. — The  syphon.  Let  A  B  C,  be  a  bent  syphon,  or  tube,  of  which  the  leg  A  B,  is  plunged 
into  a  vessel  D  E,  containing  water.  If  the  surface  of  the  water  be  F  G,  the  leg  of  the  syphon, 
A  B,  will  be  filled  w:ith  water  as  high  as  the  surface,  that  is,  up  to  H,  the  portion  H  B  C, 
remaining  full  of  air.  If,  then  the  air  be  drawn  off  by  suction  through  the  aperture  C,  the 
liquid  also  will  follow.  And  if  the  aperture  C,  be  level  with  the  surface  of  the  water,  the 
syphon,  though  full,  will  not  discharge  the  water,  but  will  remain  full:  so  that,  although  it 
is  contrary  to  nature  for  water  to  rise,  it  has  risen  so  as  to  fill  the  tube  ABC,  and  the  water 
will  remain  in  equilibrium,  like  the  beams  of  a  balance,  the  portion  H  B,  being  raised  on  high, 
and  the  portion  B  C,  suspended.  But  if  the  outer  mouth  of  the'  syphon  be  lower  than  the 
surface  F  G,  as  at  K,  the  water  flows  out,  for  the  liquid  in  K  B,  being  heavier,  overpowers 
and  draws  toward  it  the  liquid  B  H.  The  discharge,  however,  continues  only  until  the 
surface  of  the  water  is  on  a  level  with  the  mouth  K,  when,  for  the  same  reason  as  before, 
the  efflux  ceases.  But  if  the  outer  mouth  of  the  tube  be  lower  than  K,  as  at  L,  the  discharge 
continues  until  the  surface  of  the  water  reaches  the  mouth  A. 


Oues.    What  is  the  weight  of  a  cubic  foot  of  water  at  \ 
maximum  density? 

Ans.     It  is  generally  taken  at  the  figure  given  by  Rankine,  i 

62.425  lbs.*  \ 


*NOTE. — Some  authorities  give  as  low  as  62.379.  The  figure  62.5  commonly  given  is 
approximate.  The  highest  authoritative  figure  is  62.428.  At  62°  Fahr.,  the  figures  range 
from  62.291  to  62.36.  The  figure  62.355  is  generally  accepted  as  the  most  accurate,  though  for 
ordinary  calculations,  the  figure  62.4  is  generally  taken,  this  corresponding  to  the  weight  at 
53*  F. 


BASIC  PRINCIPLES 


Oues.    What  is  the  weight  of  one  U.  S.  gallon  of  water? 

Ans.     One  U.  S.  gallon  (231   cu.  ins.)   of  water  weighs  S}^ 


lbs. 


The  figure  8  H  is  correct  when  the  water  is  at  a  temperature  of  65°  Fahr* 


Fig.  5. — Hydraulic  principles;  2.  Pressure  exerted  anywhere  upon  a  mass  of  liquid  is  trans^ 
mitied  undiminished  in  all  directions,  and  acts  with  the  same  force  on  all  equal  surfaces^  and 
in  a  direction  at  right  angles  to  those  surfaces.  CD,  above  is  a  vessel  composed  of  two  cylin- 
drical parts  of  unequal  diameters,  and  filled  with  water  to  a.  The  bottom  of  the  vessel 
CD,  supports  the  same  pressure  as  if  its  diameter  were  everywhere  the  same  as  that  of  its 
lower  part;  and  it  would  at  first  sight  seem  that  the  scale  MN,  of  the  balance  in  which  the 
vessel  CD,  is  placed,  ought  to  shqw  the  same  weight  as  if  there  had  been  placed  in  it  a  cylin- 
drical vessel  having  the  same  weight  of  water,  and  having  the  diameter  of  the  part  D.  But 
the  pressure  exerted  on  the  bottom  of  the  vessel  is  not  all  transmitted  to  the  scale  MN: 
for  the  upward  pressure  upon  the  surface  n  o,  of  the  vessel  is  precisely  equal  to  the  weight 
of  the  extra  quantity  of  water  which  a  cylindrical  vessel  would  contain,  and  balances  an 
equal  portion  of  the  downward  pressure  on  m.  Consequently  the  pressure  on  the  plate  MN, 
is  simply  equal  to  the  weight  of  the  vessel  CD,  and  of  the  water  which  it  contains. 


Oues.     How  does  the  pressure  of  water  due  to  its  weighty 
vary? 

Ans.     It  varies  with  the  head,   and  is  equal  to   .43302  lbs. 
per  sq.  in.  for  every  foot  of  (static)  head. 


NOTE. — Compressibility  of  water. — Water  is  very  slightly  compressible.  Its  compres- 
sibility is  from  .00004  to  .000051  for  one  atmosphere,  decreasing  with  increase  of  temperatuie. 
For  each  foot  of  pressure,  distilled  water  will.be  diminished  in  volume  .0000015  to  .000001.3. 
Water  is  so  incompressible  that  even  at  a  depth  of  a  mile  a  cubic  foot  of  water  will  weigh  only 
about  ^2  !!>•  more  than  at  the  surface. — Kent. 


BASIC  PRINCIPLES 


'    Heat. — By  definition  heat  is  a  form  of  energy  known  by  its 

effects. 

These  effects  are  indicated  through  the  touch  and  feeHng,  as  well  as  by 
the  expansion,  fusion,  combustion  or  evaporation  of  the  matter  upon  which 
it  acts. 

Oues.     What  is  temperature? 

Ans.     That  which  indicates  how  hot  or  cold  a  substance  is; 
a  measure  of  sensible  heat. 


Fig.  6.— Method  of  judging  the  heat  of  a  soldering  bit  or  so  called  "iron,"  illustrating se/isibfe        i 
heat. 

Ones.     What  is  sensible  heat? 

Ans.     That  heat  which  produces  a  rise  of  temperature  as  dis-     ] 
tinguished  from  latent  heat.  \ 

Oues.     What  is  latent  heat?  ] 

Ans.  The  quantity  of  heat  required  to  change  the  state  or 
condition  under  which  a  substance  exists  without  changing  its 
temperature.  ] 


BASIC  PRINCIPLES 


Thus  a  definite  quantity  of  heat  must  be  transferred  to  ice  at  32°  to- 
change  it  into  water  at  the  same  temperature. 


Oues.    What  is  specific  heat? 

Ans.  The  ratio  of.  the  quantity  of  heat  required  to  raise  the 
temperature  of  a  given  weight  of  any  substance  one  degree  to 
the  quantity  of  heat  required  to  raise  the  temperature  of  the 
same  weight  of  water  from  62°  to  63°  Fahr. 


Figs.  7  to  9. — ^Three  ways  in  which  heat  is  transferred;  fig.  7,  by  radiation;  fig.  8,  by  conduction; 
fig.  9,  by  convection.  In  fig.  7,  the  water  in  the  beaker  is  heated  by  heat  rays  which  radiate 
in  straight  lines  in  all  directions  from  the  flame.  In  ng.  8,  the  flame  will  not  pass  through . 
the  wire  gauze,  because  the  latter  conducts  the  heat  away  from  the  flame  so  rapidly  that 
the  gas  on  the  other  side  is  not  raised  to  the  temperature  of  ignition.  In  fig.  9,  the  water 
nearest  the  flame  becomes  heated  and  expanded.  It  is  then  rendered  less  dense  than  the 
surrounding  water,  and  hence  rises  to  the  top  while  the  colder  and  therefore  denser  water 
from  the  sides  flows  to  the  bottom  thus  transferring  heat  by  convection  currents. 

Owes.    Explain  the  term  "transfer  of  heat." 

Ans.  When  bodies  of  unequal  temperatures  are  placed  near 
each  other,  heat  leaves  the  hot  body  and  is  absorbed  by  the  colder 
body  until  the  temperature  of  each  is  equal. 

The  rate  by  which  the  heat  is  absorbed  by  the  colder  body  is  proportional 
to  the  difference  of  temperature  between  the  two  bodies.  The  greater  the 
difference  of  temperature,  the  greater  the  rate  of  flow  of  the  heat. 


BASIC  PRINCIPLES 


Oues.    How  does  a  transfer  of  heat  take  place? 

Ans.     By  radiation,  conduction  or  convection. 

Thus,  in  a  boiler,  heat  is  given  off  from  the  furnace  fire  in  rays  which 
radiate  in  straight  Hnes  in  all  directions  being  transferred  to  the  crown  and 
sides  of  the  furnace  by  radiation;  it  passes  through  the  plates  by  con- 
duction, and  is  transferred  to  the  water  by  convection,  that  is,  by  currents. 


Fig.  10. — Diagram  showing  principle  and  construction  of  the-  Whitney  hot  wire  instruments 
illustrating  expansion  by  the  action  of  heat.  The  action  of  instruments  of  this  type 
depends  on  the  heating  of  a  wire  by  the  passage  of  a  current  causing  the  wire  to  lengthen. 
This  elongation  is  magnified  by  suitable  mechanism  and  transmitted  to  the  pointer  of  the 
instrument. 


Oues.    What  is  an  important  effect  of  heat? 

Ans.  Bodies  expand  by  the  action  of  heat.  For  instance, 
boiler  plates  are  riveted  with  red  hot  rivets  in  an  expanded 
state;  on  cooling  the  rivets  contract  and  draw  the  plates  to- 
gether with  great  force  making  a  tight  joint. 

An  exception  to  the  rule,  it  should  be  noted,  is  water,  which  contracts 
as  it  is  heated  from  the  freezing  point  32°  Fahr.,  to  the  point  of  maximum 
density  39.1°;  at  other  temperatures  it  expands. 


8 


BASIC  PRINCIPLES 


Heat    and    Work. — Heat    develops    mechanical  force,    and 
motion,  hence  it  is  convertible  into  mechanical  work, 

Oues.     How  can  heat  be  measured  ? 

Ans.     By  a  standard  unit  called  the  British  unit  of  heat, 
or  British  thermal  unit  (B.',u,), 

Ques.    What  is  the  British  thermal  unit? 

Ans.     The  heat  required  to  raise  one  pound  of  water  from 
62°  to  63°  Fahr.  (Peabody). 


I  LB.  OF  WATER 
AT  32  •  FAHR 


I  LB.  OF  WATER 
AT  212'  FAHR. 


Figs.  11  and  12. — Experiment  illustrating  the  British  thermal  unit.  Place  one  pound  of  water 
at  32°  Fahr.  into  a  beaker  over  a  Bunsen  burner  as  in  fig.  11  assuming  no  loss  of  heat  from 
the  water.  It  will,  according  to  the  definition,  require  180  heat  units  to  heat  the  water  from 
32°  to  212°  Fahr.  Now,  if  the  transfer  of  heat  take  place  at  a  uniform  rate  and  it  require, 
say  five  minutes  to  heat  the  water  to  212°,  then  one  heat  unit  will  be  transferred  to  the 
water  in  (5  X60)  -t-180  =2  seconds. 

Ques.     What  is  the  mean  British  thermal  unit? 

Ans.     ^  180  part  of  the  heat  required  to  raise  the  temperature  of 
one  pound  of  water  from  32°  to  212°  Fahr.^  f 


*NOTE. — The  old  definition  of  the  heat-unit  (Rankine),  viz.,  the  quantity  of  heat  re- 
quired to  raise  the  temperature  of  1  lb.  of  water  1°  Fahr.,  at  or  near  its  temperature  of  maximum 
density  (39.1°  F.)  was  the  standard  till  1909. 

tNOTE. — By  Peabody's  definition,  the  heat  required  to  raise  1  lb.  of  water  from  32°  to 
212°  is  180.3  instead  of  180  units,  and  the  latent  heat  at  212°  is  969.7  instead  of  970.4. 


BASIC  PRINCIPLES 


It  should  be  noted  that  this  is  the  definition  adopted  in  this  work  for  the 
British  thermal  unit  (B.  t.  u.),  corresponding  to  the  unit  used  in  the  Marks 
and  Davis  steam  tables,  which  is  now  the  recognized  standard. 

Owes.    What  is  work? 

Ans.     The  overcoming  of  resistance  through  a  certain  distance 
by  the  expenditure  of  energy.  ^  '     , 

Oues.     How  can  work  be  measured? 

Ans.     By  a  standard  unit  called  the  foot  pound. 


■^^m 


Fig.  13. — Experiment  showing  relation  between  heat  and  work.  Take  a  brass  tube  A  B,  at- 
tached to  a  spindle  geared  to  rotate  rapidly  and  partly  fill  the  tube  with  water  and  insert  a 
cork.  Apply  a  friction  clamp  D,  and  rapidly  rotate  the  tube  by  turning  the  wheel  C.  The 
energy  expended  in  overcoming  the  friction  due  to  the  clamp  and  rotating  the  tube  causes 
the  water  to  heat  and  finally  boil;  if  continued  long  enough,  the  pressure  generated  will  expel 
the  cork.    During  the  operation  work  has  been  transformed  into  heat. 


Oues.    What  is  a  foot  pound? 

Ans.  It  is  the  amount  of  work  done  in  raising  one  pound  one 
foot,  or  in  overcoming  a  pressure  of  one  pound  through  a  distance 
of  one  foot. 

Thus,  if  a  5  pound  weight  be  raised  10  feet,  the  work  done  is  5X10  =  50 
foot  pounds. 


12  BASIC  PRINCIPLES 


A  body  may  possess  energy  whether  it  do  any  work  or  not,  but  no  work 
is  ever  done  except  by  the.  expenditure  of  energy.  There  are  two  kinds  of 
energy : 

1.  Potential  energy; 

2.  Kinetic  energy. 

Potential  energy  is  energy  due  to  position,  as  represented,  for  instance, 
by  a  body  of  water  stored  in  an  elevated  reservoir,  capable  of  doing  work 
by  means  of  a  water  wheel. 

Kinetic  energy  is  energy  due  to  momentum,  that  is  to  say,  the  energy  of 
a  moving  body. 

Conservation  of  Energy. — The  doctrine  of  physics,  that 
energy  can  be  transmitted  from  one  body  to  another  or  trans- 
formed in  its  manifestations,  but  may  neither  he  created  nor 
destroyed. 

Energy  may  be  dissipated,  that  is,  converted  into  a  form  from  which  it 
cannot  be  recovered,  as  is  the  case  with  the  great  percentage  of  heat 
escaping  with  the  exhaust  of  a  locomotive,  or  the  condensing  water  of  a 
steamship,  but  the  total  amount  of  energy  in  the  universe,  it  is  argued, 
remains  constant  and  invariable. 

Thus,  in  Joule's  experiment,  fig.  14,  the  potential  energy  of  the  weights 
is  not  lost,  but  is  transformed  into  heat,  which  is  one  form  of  energy. 
The  apparatus  possesses  the  same  amount  of  energy  at  the  end  as  at  the 
beginning  of  the  experiment,  but  the  distribution  of  the  energy  has  been 
changed,  that  is  the  potential  energy  given  up  by  the  weight  has  been 
transformed  into  heat,  raising  the  temperature  of  the  water. 

Power. — By  definition,  power  is  the  rate  at  which  work  is 
done;  in  other  words,  it  is  work  divided  by  the  time  in  which 
it  is  done. 

The  unit  of  power  in  general  use  is  the  horse  power "^  which 
is  defined  as  33,000  joot  pounds  per  minute. 

That  is,  one  horse  power*  is  required  to  raise  a  weight  of 

33,000  pounds  1  foot  in  one  minute 

3,300  pounds         10  feet  in  one  minute 

33  pounds    1,000  feet  in  one  minute 

3.3  pounds  10,000  feet  in  one  minute 

1  pound   33,000  feet  in  one  minute 

etc. 


*NOTE. — The  term  "horse  power" ._  ^ „ 

power  of  a  strong  London  draught  horse  to  do  work  during  a  short  interval,  and  used  it  as  a 
power  rating  for  his  engine* 


BASIC  PRINCIPLES 


13 


60ILIN6  INCHES 

POINT  OF 

DE6.FAHR.     MERCURY 


Pressure. — According  to 
Rankine,  the  term  pressure,  in 
the  popular  sense,  which  is  also 
the  sense  generally  employed  in 
applied  mechanics,  is  used  to 
denote  a  force,  of  the  nature  of  a 
thrust,  distributed  over  a  surface; 
in  other  words,  the  kind  of 
force  with  which  a  body  tends 
to  expand,  or  resists  an  effort  to 
compress  it. 

In  the  definition  it  should  be  care- 
fully noted  that  the  pressure  is  con- 
sidered as  distributed  over  a  surface. 

The  pressure  distributed  over  a 
surface  is  usually  stated  in  terms  of 
the  pressure  distributed  over  a  unit 
area  of  the  surface,  as  pounds  per 
square  inch,  meaning  that  a  press- 
ure of  a  given  number  of  pounds  is 
distributed  over  each  square  inch  of 
surface.  This  should  be  very  clearly 
understood  by  the  engineer,  as  fur- 
ther explained  in  figs.  18  and  19. 


Fig.  17. — Mercurial  barometer,  illustrating 
the  boiling  point  for  various  pressures. 


NOTE. — Boiling    point    of    various    sub- 
stances at  atmospheric  pressure  (14.7  lbs.): 

Ether,  sulphide 100°  P^'ahr. 

Carbon  bisulphide US''      " 

Chloroform 140"      " 

Bromine 145°      " 

Wood  spirit 150°     " 

Alcohol 173°      " 

Benzine 176°      « 

Water 212°      ^ 

Average  sea  water 213.2° 

Saturated  brine 226°      " 

Nitric  acid 248°      " 

Oil  of  turpentine 315*   '  " 

Aniline 363° 

Naphthaline 428°      ^ 

Phosphorus ^^o      « 

Sulphuric  acid ^^^^ 

Linseed  oil ^^^o      « 

Mercury 676° 

Sulphur •  800° 


10 


BASIC  PRINCIPLES 


Ones.  What  is  the  relation  between  the  unit  of  heat 
and  the  unit  of  work? 

Ans.  It  was  shown  by  experiments  made  by  Joule  (1843-50) 
that  1  unit  of  heat  =  772  units  of  work.  This  is  known  as  the 
* 'mechanical  equivalent  of  heat"  or  Joule* s  equivalent.  ' 

More  recent  experiments  by  Prof.  Rowland  (1880)  and  others  give 
higher  figures;  778  is  generally  accepted,  but  777.5  is  probably  more  nearly 
correct,  the  value  777.52  being  used  by  Marks  and  Davis  in  their  steam  tables. 

The  value  778  is  sufficiently  accurate  for  ordinary  calculations. 


Fig.  14. — The  mechanical  equivalent  of  heat.  In  1843,  Dr.  Joule  of  Manchester,  England , 
performed  his  classic  experiment,  which  revealed  to  the  world  the  mechanical  equivalent 
of  heat.  As  shown  in  the  figure,  a  paddle  was  made  to  revolve  with  as  little  friction  as  possible 
in  a  vessel  containing  a  pound  of  water  whose  temperature  was  known.  The  paddle  was 
actuated  by  a  known  weight  falling  through  a  known  distance.  A  pound  falling  through  a 
distance  of  one  foot  represents  afoot  Pound  of  work.  At  the  beginning  of  the  experiment  a 
thermometer  was  placed  in  the  water,  and  the  temperature  noted.  The  paddle  was  made 
to  revolve  by  the  falling  weight.  When  772  foot  pounds  of  energy  had  been  expended  on 
the  pound  of  water,  the  temperature  of  the  latter  had  risen  one  degree,  and  the  relationship 
between  heat  and  mechanical  work  was  found;  the  value  772  foot  pounds  is  known  as  Joule's 
equivalent.  More  recent  experiments  give  higher  figures,  the  value  778,  is  now  generally  ; 
used  but  according  to  Kent  777.62  is  probably  more  nearly  correct.  Marks  and  Davis  in 
their  steam  tables  have  used  the  figure  777.52. 

Joule's  Experiment. — In  fig.  14,  a  weight  W  is  attached  to 
a  cord  which  passes  over  a  pulley  R,  and  is  wound  around  a 
revolving  drum  B.  Attached  to  the  drum  is  a  spindle  having 
fastened  at  its  lower  end  vanes  or  paddles  P  P  made  of  thin 


BASIC  PRINCIPLES 


11 


pieces  of  sheet  metal.     These  paddles  are  immersed  in  a  vessel 
V,  containing  a  definite  quantity  of  water. 

In  operation,  as  the  weight  W,  falls,  the  paddles  rotate  in  the  water,  the 
water  itself  being  kept  from  rotating  by  fixed  pieces  not  shown.  It  was 
discovered  that  the  work  done  by  the  weight  in  descending,  was  not 
lost  but  appeared  as  heat  in  the  water,  the  agitation  of  the  paddles  having 
increased  the  temperature  of  the  water  by  an  amount  which  can  be  meas- 
ured by  a  thermometer. 


ELEVATED 
TANK 


y 


BHiBBBiiBBaaBEl, 

i.||.i  lull kIi.IiiIiii  .iI-  I..  ,:i'llii|,illl.:,l|i"|M 


TiC^=^ 


ES- 


^ 


35 


DVNAMO       STORAGE  BATTERY 

Figs.  15  and  16. — Potential,  and  kinetic  energy.  In  fig.  15,  the  water  stored  in  the  elevated  tank 
possesses  energy  by  virtue  of  its  position;  being  higher  than  the  water  wheel,  the  water 
will  flow  by  gravity  through  the  pipe  and  do  work  on  the  wheel.  Thus,  the  potential  energy 
of  the  water  at  rest  in  the  tank,  is,  when  it  flows  through  the  pipe  converted  into  kinetic 
energy  which  is  spent  on  the  wheel.  Fig  16  represents  a  railway  car  with  axle  lighting  system. 
If  the  car  be  set  in  motion  and  then  no  further  power  be  applied  its  momentum  or  kinetic 
energy  will  drive. the  dynamo  which  in  turn  will  charge  the  storage  battery,  and  acting  like 
a  brake  will  gradually  bring  the  car  to  rest.  During  this  operation,  the  kinetic  energy, 
originally  possessed  by  the  moving  car,  is  absorbed  by  the  dynamo  (neglecting  friction) 
and  delivered  to  the  battery  as  electrical  energy  which  may  be  used  in  lighting  the  car. 

By  numerous  experiments,  Joule  determined  with  the  utmost  care  that 
one  pound  of  water  was  increased  in  temperature  one  degree  by  the  work 
done  on  it  during  the  descent  of  772  pounds  through  one  foot. 

This  value,  as  before  mentioned,  is  too  small  for  ordinary  calculation, 
the  value  778,  the  generally  accepted  standard,  should  be  used;  the  value 
777.52  is  probably  more  nearly  correct. 


Energy. — By  definition,  energy  is  stored  work,  that  is,  the 
ability  to  do  work,  or  in  other  words,  to  move  against  resistance. 


12  BASIC  PRINCIPLES 


A  body  may  possess  energy  whether  it  do  any  work  or  not,  but  no  work 
is  ever  done  except  by  the.  expenditure  of  energy.  There  are  two  kinds  of 
energy : 

1.  Potential  energy; 

2.  Kinetic  energy. 

Potential  energy  is  energy  due  to  position,  as  represented,  for  instance, 
by  a  body  of  water  stored  in  an  elevated  reservoir,  capable  of  doing  work 
by  means  of  a  water  wheel. 

Kinetic  energy  is  energy  due  to  momentum,  that  is  to  say,  the  energy  of 
a  moving  body. 

Conservation  of  Energy. — The  doctrine  of  physics,  that 
energy  can  be  transmitted  from  one  body  to  another  or  trans- 
formed in  its  manifestations,  but  may  neither  he  created  nor 
destroyed. 

Energy  may  be  dissipated,  that  is,  converted  into  a  form  from  which  it 
cannot  be  recovered,  as  is  the  case  with  the  great  percentage  of  heat 
escaping  with  the  exhaust  of  a  locomotive,  or  the  condensing  water  of  a 
steamship,  but  the  total  amount  of  energy  in  the  universe^  it  is  argued, 
remains  constant  and  invariable. 

Thus,  in  Joule's  experiment,  fig.  14,  the  potential  energy  of  the  weights 
is  not  lost,  but  is  transformed  into  heat,  which  is  one  form  of  energy. 
The  apparatus  possesses  the  same  amount  of  energy  at  the  end  as  at  the 
beginning  of  the  experiment,  but  the  distribution  of  the  energy  has  been 
changed,  that  is  the  potential  energy  given  up  by  the  weight  has  been 
transformed  into  heat,  raising  the  temperature  of  the  water. 

Power. — By  definition,  power  is  the  rate  at  which  work  is 
done;  in  other  words,  it  is  work  divided  by  the  time  in  which 
it  is  done. 

The  unit  of  power  in  general  use  is  the  horse  power "^  which 
is  defined  as  33,000  foot  pounds  per  minute. 

That  is,  one  horse  power*  is  required  to  raise  a  weight  of 

33,000  pounds  1  foot  in  one  minute 

3,300  pounds         10  feet  in  one  minute 

33  pounds    1,000  feet  in  one  minute 

3.3  pounds  10,000  feet  in  one  minute 

1  pound   33,000  feet  in  one  minute 

etc. 


*NOTE. — The  term  "horse  power"  is  due  to  James  Watt,  who  figured  it  to  represent  the 
power  of  a  strong  London  draught  horse  to  do  work  during  a  short  interval,  and  used  it  as  a 
power  rating  for  his  engine* 


BASIC  PRINCIPLES 


13 


601HN6  INCHES 


POINT               OF 
16.FAHR.    MERCURY 

31 

2ia 

29.921  - 

209.55 

2850  - 

205.87 

26.47  - 

201.96 

24.43  - 

197.75 

22.40- 

195.22 

20.56- 

188.27 

18.32- 

182.86 

16.29- 

176.85 

14.25  - 

170.06 

12.22  - 

162.28       10.18 


ABSOLUTE 
PRESSURE 
LBS.PERSO.IN. 

-15.226 

-14.696 

-14 

13 

-12 


-  II 


10 


-    9 


o 


o 


Pressure. — According  to 
Rankine,  the  term  pressure^  in 
the  popular  sense,  which  is  also 
the  sense  generally  employed  in 
applied  mechanics,  is  used  to 
denote  a  force,  of  the  nature  of  a 
thrust,  distributed  over  a  surface; 
in  other  words,  the  kind  of 
force  with  which  a  body  tends 
to  expand,  or  resists  an  effort  to 
compress  it. 

In  the  definition  it  should  be  care- 
fully noted  that  the  pressure  is  con- 
sidered as  distributed  over  a  surface. 

The  pressure  distributed  over  a 
surface  is  usually  stated  in  terms  of 
the  pressure  distributed  over  a  unit 
area  of  the  surface,  as  pounds  per 
square  inch,  meaning  that  a  press- 
ure of  a  given  number  of  pounds  is 
distributed  over  each  square  inch  of 
surface.  This  should  be  very  clearly 
understood  by  the  engineer,  as  fur- 
ther explained  in  figs.  18  and  19. 


32 
0 


Fig.  17. — Mercurial  barometer,  iMustrating 
the  boiling  point  for  various  pressures. 


NOTE. — Boiling    point    of    various  sub- 
stances at  atmospheric  pressure  (14.7  lbs.): 

Ether,  sulphide 100°  Fahr. 

Carbon  bisulphide 118°      " 

Chloroform 140°      " 

Bromine 145°  " 

Wood  spirit 150°  " 

Alcohol 173°  '^ 

Benzine 176°  " 

Water 212°  ^ 

Average  sea  water 213.2° 

Saturated  brine 226° 

Nitric  acid " 248°      ^ 

Oil  of  turpentine 315* 

Aniline 363°      "" 

Naphthaline 428°      ** 

Phosphorus 554°      " 

Sulphuric  acid 590°      " 

Linseed  oil 597°      |^ 

Mercury 676°      " 

Sulphur 800°      " 


16 


BASIC  PRINCIPLES 


Pressure  Scales. — The  term  vacuum  is  a  much  abused  word; 

strictly  speaking  it  is  defined  as  a  space  devoid  of  matter.     This 
is  equivalent  to  saying  a  space  in  which  the  pressure  is  zero. 


Figs.  21  and  22.  Bent  tube  and  diaphragm  of  corrugated  metal  as  used  in  two  types  of 
steam  gauge.  In  the  one  class,  the  pressure  of  the  steam  acts  upon  diaphragms  or  plates 
of  some^  kind,  shown  in  fig.  21,  which  represents  a  section  of  a  pair  of  metal  plates,  A  A, 
of  this  kind.  These  are  made  with  circular  corrugations,  a^  shown  in  section  and  also  by  the 
shading.  The  steam  enters  by  the  pipe  c,  and  fills  the  chamber  between  the  metal  plates 
or  diaphragms.  The  corrugations  of  the  latter  give  them  sufficient  elasticity,  so  that  when 
the  pressure  is  exerted  between  them  they  will  be  pressed  apart  by  the  steam.  If  they  were 
flat,  it  is  plain  that  they  would  not  yield,  or  only  to  a  very  slight  degree,  to  the  pressure  of 
the  steam.  In  the  other  class  of  gauge,  the  steam  acts  upon  a  bent  metal  tube  of  a  flattened 
or_ elliptical  section,  such  as  shown  in  fig.  22.  The  pressure  has  a  tendency  to  straighten 
this  tube,  and  this  straightening  tendency  is  directly  proportioned  to  the  pressure;  the  free 
end  of  this  tube  is  connected  through  suitable  gearing  to  the  pointer  or  hand. 


The  word  vacuum  has  come,  by  ill  usage  to  mean  any  space  in 
which  the  pressure  is  less  than  that  of  the  atmosphere,  and  ac- 
cordingly, it  is  necessary  to  accept  the  latter  definition. 


BASIC  PRINCIPLES 


17 


This  gives  rise  to  two  scales  of  pressure: 


1.  Gauge  pressure; 

2.  Absolute  pressure. 


Fig.  23. — Elementary  boiler 
or  closed  vessel  illustrating 
the  difiference  between 
gauge,  and  absolute  pres- 
sure. 


When  the  hand  of  a  steam  gauge 
is  at  zero,  the  pressure  actually 
existing  is  14.73  lbs.  (referred  to  a 
30  inch  barometer)  or  that  of  the 
atmosphere.  The  scale  in  the  gauge 
is  not  marked  at  this  point  14.73  lbs. 
but  zero  because  m  the  steam  boiler 
as  well  as  any  other  vessel  under 
pressure,  the  important  measure- 
ment is  the  difference  of  pressure 
between  the  inside  and  outside. 
This  difference  of  pressure  or  eff ec  - 
tive  pressure  for  doing  work  is  called 
the  "gauge  pressure"  because  it  is 
measured  by  the  gauge  on  the  boiler. 
The  second  pressure  scale  is  known 
as  absolute  pressure,  because  it  gives 
the  actual  pressure  above  zero.  In  all 
calculations  relative  to  the  expansion 
of  steam  the  absolute  pressure  scale 
must  be  used. 


Oues,     How  is  gauge  pres- 
sure   expressed    as   absolute 


pressure  r 


Ans.     By  adding  14.73,  or  for  ordinary  calculations,  14.7  lbs.  ' 

Thus  80  lbs.  gauge  pressure  =  80 +  14.7  =94.7  lbs.  absolute  pressure. 


Oues.     How  is  absolute  pressure  expressed   as  gauge 
pressure. 

Ans.     By  subtracting  14.7. 


18 


BASIC  PRINCIPLES 


INCHES 

OF 
MERCURY 
31- 

Z9SZ\* 
f     29 
28 
27- 
26- 
25 
24 
23  H 
22 
21  - 
20 
19- 
18 
17 
16- 
15 
14 
13 
12 
I  I 
10 
9 
8 
7 
6 
5 


ABSOLUTE 
PRESSURE 
PER.SQ.IN. 

-15.226 

-^14.696 

•14 

13 

-12 

-II 

10 

9 

8 

7 

(o 

5 

4 

3 


Fig.  24. — Mercurial  barom- 
eter illustrating  the  relation 
between  "inches  of  mercury" 
and  absolute  pressure  in 
lbs.  per  sq.  in. 


Thus  90  lbs.  absolute  pressure  =  90  —  14.7 
=  75.3  lbs.  gauge  pressure. 


Oues.  How  are  pressures  below 
that  of  the  atmosphere  usually 
expressed  ? 

Ans.  As  pounds  per  square  inch  in 
making  calculations,  or  the  equivalent 
in  ''inches  of  mercury"  in  practice. 

Thus,  in  the  engine  room,  the  expression 
"28  inch  vacuum"  would  signify  an  absolute 
pressure  in  the  condenser  of  .946  lb.  per  sq.  in. 
absolute,  that  is  to  say,  the  mercury  in  a 
mercury  column  connected  to  a  condenser 
having  a  28  inch  vacuum,  would  rise  to  a 
height  of  28  inches,  representing  the  difference 
between  the  pressure  of  the  atmosphere  and 
the  pressure  in  the  condenser,  or 

14.73— .946  =  13.784  lbs. 
referred  to  a  30  inch  barometer. 

Oues.  What  is  the  meaning  of 
the  term  "referred  to  a  30  inch 
barometer?" 

Ans.  It  means  that  the  variable 
pressure  of  the  atmosphere  is  in  value 
such  that  it  will  cause  the  mercury  in 
the  barometer  to  rise  30  inches. 

Oues.  How  is  the  pressure  in 
pounds  per  square  inch  obtained 
from  the  barometer  reading? 

Ans.  Barometer  reading  in  inches  X 
.49 116  =  pressure  per  sq .  inch. 


BASIC  PRINCIPLES 


19 


Thus,  a  30  inch  barometer  reading  signifies  a  pressure  of 

.491 16  X30  =  14.74  lbs.  per  sq.  in. 
The  following  table  gives  the  pressure  of  the  atmosphere  in  pounds  per 
square  inch  for  various  readings  of  the  barometer. 

Pressure  of  the  atmosphere  per  square  inch  for  various  readings  of 

the  barometer: 

Rule. — Barometer  in  inches  of  mercury  XA9116= lbs,  per  sq.  i?i. 


Barometer 

Pressure 

Barometer 

Pressure 

(ins.  of  mercury) 

per  sq.  ins.,  lbs. 

(ins.  of  mercury) 

per  sq.  ins.,  lbs. 

28.00 

13.75 

29.921 

14.696 

28.25 

13.88 

30.00 

14.74 

28.50 

14.00 

30.25 

14.86 

28.75 

14.12 

30.50 

14.98 

29.00 

14.24 

30.75 

15.10 

29.25 

14.37 

31.00 

15.23 

29.50 

14.49 

29.75 

14.61 

The  above  table  is  based  on  the  standard  atmosphere,  which  by  defin- 
ition =29.921  ins.  of  mercury  =  14.696  lbs.  per  sq.  in.,  that  is  1  in.  of 
mercury  =  14.696-^29.921  =  .49116  lbs.  per  ^q.  in. 

Temperature  Scales. — Temperature  is  a  measure  of  sensible 
heat,  that  is,  the  temperature  of  a  substance  indicates  how  hot 
or  cold  it  is. 


The  instrument  for  measuring  temperature  is  the  well  known  ther- 
mometer. Briefly,  it  consists  of  a  hollow  stem  of  tube  of  glass  with  an 
enlargement  or  bulb  at  the  foot  filled  with  mercury  which  expands  into 
the  tube.  ^  The  stem  being  uniform  in  bore,  and  the  apparent  expansion  of 
mercury  in  the  tube  being  equal  for  equal  increments  of  temperature,  it 
follows  that  if  the  scale  be  graduated  with  equal  intervals,  these  will  indicate 
equal  increments  or  "degrees"  of  temperature. 

There  are  three  kinds  of  thermometer  scales  in  general  use: 

1.  Fahrenheit; 

2.  Centigrade; 
S.  Reaumur.  . 


20 


BASIC  PRINCIPLES 


The  relation  between  these  scales  is  shown  in  figs.  25  to  27.  3 

The  Fahrenheit  scale  is  generally  used  in  English  speaking  countries,  : 
the  freezing  point  is  32°,  and  boiling  point,  212°.  ^ 

The  Centigrade  scale  is  used  in  France.  The  freezing  point  is  0°,  and  " 
boiling  point,  100°.  j 

The  Reaumur  scale  is  used  in  Russia,  Sweden,  Turkey  and  Egypt.  \ 
The  freezing  point  is  zero  and  boiling  point  80°.  ■     ; 

Fahrenheit  is  converted  into  Reaumur  by  deducting  32°  and  taking  ; 
four-ninths  of  the  remainder,  and  Reaumur  into  Fahrenheit  by  multi-  : 
plying  by  nine-fourths,  and  adding  32°  to  the  product.  \ 


100 


75 

50 

25 
0 


212 


167 
122 

77 

32 


80 


BOILING   POINT 
~     OF  WATER 


60 


40 


20 


FREEZING  POINT 
OF  WATER 


Figs.  25  to  27. — Various  thermometer  scales.  Fig  25,  Centigrade;  fig.  26,  Fahrenheit;  fig. 
27,  Reaumur.  From  the  figure  the  scales  may  be  clearly  compared,  and  degr'^es  converted 
from  one  scale  to  another  without  calculation. 


Centigrade  temperatures  are  converted  into  Fahrenheit  temperatures 
by  multiplying  the  former  by  9,  dividing  by  5,  and  adding  32°  to  the 
quotient;  and  conversely,  Fahrenheit  temperatures  are  converted  into 
Centigrade  by  deducting  32°  and  taking  5-9ths  of  the  remainder. 

R.eaumur  degrees  are  multiplied  by  five-fourths  to  convert  them  into  the 
equivalent  Centigrade  degrees;  conversely,  four-fifths  of  the  number  of 
Centigrade  degrees  give  their  equivalent  in  Reaumur  degrees. 


I 


BASIC  PRINCIPLES 


21 


Steam. — It  has  been  stated  that  steam  is  the  medium  or 

working  substance  by  which  some   of  the  heat  energy,   liberated 
from  the  fuel  by  combustion  is    transmitted  to   the   engine   and 
J}artly  converted  into  mechanical  work, 
'    rv 

Owing  to  the  peculiarities  of  steam, 

it   is  important  that  engine  operators 

should    know    its    exact    nature 

^  ""^^--^.^^^      or  behavior  under  different 

vD  ^  "      ^"^^"-^        conditions. 


AB5.  675"  493^^59.6^  Q^ 

Fig.  28. — -Graphical  method  of  determining  the  absolute  zero.  It  is  found  by  experiment  that 
when  air  is  heated,  or  cooled  under  constant  pressure,  its  volume  increases  or  decreases  in 
such  a  way  that  if  the  volume  of  the  gas  at  freezing  point  of  water  be  1  cu.  ft.,  then  its  volume 
when  heated  to  the  boiling  point  of  water,  will  have  expanded  to  1.3654  cu.  ft.  Or,  inversely, 
if  the  volume  remain  c'onstant,  and  the  pressure  exerted  by  the  gas  at  freezing  point  =  1 
atmosphere,  then  the  pressure  at  boiling  point  of  water  =  1.3654  atmospheres.  These  results 
may  be  set  out  in  the  form  of  a  diagram,  as  here  shown.  In  construction,  draw  a  vertical 
line  to  represent  temperatures  to  any  scale,  and  mark  on  it  points  representing  the  freezing 
point  and  boiling  point  of  water,  marked  32°  and  212°  respectively.  From  32°  set  out,  at 
right  angles  to  the  line  of  temperature,  a  line  of  pressure  AB  =  1  atmosphere  to  any  scale, 
and  at  212°  a  line  CD  =  1.3654  atmospheres  to  the  same  scale.  Join  the  extremities  DB, 
of  these  lines  to  intersect  the  line  of  temperatures.  It  is  assumed  by  physicists  that,  since 
the  pressures  vary  regularly  per  degree  of  change  of  temperature  between  certain  limits 
within  the  range  of  experiment,  they  vary  also  at  the  same  rate  beyond  that  range,  and, 
therefore,  that  the  point  of  intersection  of  the  straight  line  DB,  produced  gives  the  point  at 
which  the  pressure  is  reduced  to  zero,  this  point  being  known  as  the  absolute  zero. 


NOTE. — Absolute  temperature. — This  is  defined  as  the  actual  temperature  of  anything 
reckoned  from  absolute  zero.  It  is  taken  as  the  teniperature  indicated  by  the  thermometer  or 
similar  instrument,  to  which  is  added  273.1°  centigrade  or  459,6°  Fahrenheit,  the  difference 
between  absolute  zero  and  the  zeros  of  the  respective  thermo metric  scales,  which  are  arbi- 
trarily fixed. 

NOTE. — Absolute  zero. — In  physics,  temperature  or  the  heat  which  it  represents  is 
regarded  as  a  manifestation  of  rnolecular  activity  in  any  substance,  the  higher  the  tempera- 
ture, the  greater  the  motion  or  vibration  among  the  molecules  of  which  every  solid,  liquid  or 
gaseous  body  is  composed.    Experiments  have  demonstrated  that  a  gas  expands  when  at  the 

freezing  point  and  under  constant  pressure  about   -„.       of  its  volume  for  each  increase  of  1" 

Fahr.  in  pressure.  This  tends  to  show,  that  at  some  point  about  491.6° — 32°  or  459.6°  below 
zero  or  Fahrenheit's  scale,  tfee  volume  of  the  gas  would  have  become  zero  or  it  would  have  lost 
all  the  molecular  vibration  which  manifests  itself  as  heat.  The  temperature  of  this  absolute 
zero  point,  from  which  all  temperatures  of  gases  are  reckoned,  is  estimated  at — 273.1°  C.  or 
-7-459.6°  F.  The  lowest  temperatures  yet  obtained  by  anyone  are  those  at  which  hydrogen 
liquifies,  — 423°  F.,  and  its  freezing  point,  430.6°  F. 


22 


BASIC  PRINCIPLES 


Oues.    What  is  steam? 

Ans.     Steam  is  the  vapor  of  water. 

It  is  a  colorless,  expansive,  invisible  fluid.  The  white  cloud  seen  issuing 
from  an  exhaust  pipe,  and  usually  called  steam,  is  not  steam  but  in  reality 
a  fog  of  minute  liquid  particles  produced  by  condensation. 


X 


Fig.  29. — The  various  states  of  steam  as  exemplified  in  the  operation  of  a  safety  valve.  By 
closely  observing  a  safety  valve  when  blowing  off,  as  for  instance  the  safety  valve  on  a  loco- 
motive, or  better  the  safety  valve  on  a  marine  boiler,  furnishing  superheated  steam,  very 
interesting  phenomena  can  be  observed.  At  A,  very  close,  the  escaping  gas  is  entirely 
invisible  being  at  this  point  superheated.  At  B,  the  outline  of  the  ascending  column  is  seen, 
the  interior  being  invisible  and  gradually  becoming  "foggy"  and  as  the  vapor  ascends 
from  B  to  D,  denoting  the  gradual  reduction  in  temperature,  the  steam  becoming  saturated 
and  superheated  or  wet,  reaching  the  white  state  at  D,  where  it  is  popularly  and  erroneously 
known  as  "steam."  Steam  is  invisible.  The  reason  the  so  called  wet  steam  can  be  seen  is 
because  wet  steam  is  a  mechanical  mixture  made  up  of  saturated  steam  which  is  invisible, 
and  which  holds  in  suspension  a  multiplicity  of  fine  water  globules  formed  by  condensation; 
it  is  the  collection  of  water  globules  or  condensate  that  is  visible. 

Oues.     How  is  steam  classified  according  to  its  quality? 

Ans.     As  wet,  dry^  saturated,  superheated,  or  gaseous. 


BASIC  PRINCIPLES 


23 


Fig.  30.* — The  phenomena  of  vaporization.  When  heat  is  applied  to  water  in  a  vessel  as 
shown,  it  is  conducted  through  the  heating  surface  to  the  lower  state  which  gradually  be- 
comes heated  to  the  boiling  point.  This  is  followed  by  the  formation  of  globules  of  steam 
on  the  heating  surface  indicatmg  that  particles  of  the  water  have  received  a  supply  of  heat 
equal  to  the  sensible  and  latent  heat  of  steam  at  the  pressure  existing  at  the  bottom  of  the 
vessel,  thus  a  change  cf  slate  has  taken  place,  and  this  may  be  called  initial  vaporization 
as  distinguished  from  vaporization  or  the  completion  of  the  process.  As  more  heat  is  added, 
more  of  the  water  adjacent  to  the  globules  is  converted  into  steam  which  causes  the  globules 
to  increase  in  size  until  their  buoyancy  becomes  sufhcient  to  overcome  the  tension  with  the 
heating  surface  and  imtial  disengagement  takes  place.  Following  the  course  of  a  globule  dis- 
engaging from  the  central  and  hottest  portion  of  the  heating  surface,  it  rapidly  rises  to  the 
surface,  and  expands  as  it  rises  because  the  pressure  gradually  decreases  due  to  diminishing 
head  of  water.  On  reaching  the  disengaging  surface,  a  bubble  is  formed  which  at  once  bursts 
as  the  water  closes  in  behind  the  steam  contained  in  the  bubble,  thus  completing  the  process 
of  vaporization  of  the  original  particles  of  water;  that  is  to  say,  a  change  of  state  has  taken 
place  and  the  steam  has  been  disengaged  from  the  water. 

NOTE. — It  should  be  noted  in  the  above  illustration  that  all  of  the  steam  globules  formed 
on  the  heating  surface  do  not  reach  the  surface,  as  for  instance,  the  globule  A,  found  near  the 
side  of  the  vessel  will,  as  it  rises,  take  same  course  as  Al,  A2,  A3,  expanding  as  it  rises.  After 
passing  the  portion  A3,  it  may  be  deflected  over  toward  the  side  of  the  vessel  into  relatively 
■  cold  water  as  indicated  by  the  arrow,  giving  up  its  heat  to  the  cold  water,  resulting  in  conden- 
sation and  the  gradual  collapse  of  the  globule  as  indicated.  It  should  be  noted  further  that 
the  pressure  at  the  bottom  of  the  vessel  or  heating  surface  being  greater  than  the  pressure  at 
the  disengaging  surface,  the  temperature  at  which  initial  vaporization  takes  place  is  greater 
than  that  of  vaporization  proper. 


24 


BASIC  PRINCIPLES 


Wet  steam  contains  intermingled  moisture,  mist  or  spray,  and  has  th^ 
same  temperature  as  dry  saturated  steam  of  the  same  pressure.  \ 

Dry  steam  contains  no  moisture;  it  may  be  either  saturated  or  super-^ 
heated.  *  r. 

Saturated  steam  is  steam  of  a  temperature  due  to  its  pressure.  I 

^Superheated  steam  is  steam  having  a  temperature  above  that  due  to  itsj 


pressure. 


|SJ  STATE 


"i  \    (ICE) 


VSOLID 

J 


-l. 


fusion; 


^IST  CHANGE. 
,        OF  STATE. 


'''U 

~'^^-'^'. 


' '  i^ 


;^4^n'3'??5JArE 

GAS 

(STLAM) 


2':'?  STATE 

VAPORIZATION  — 


f-LIQUID 

(WATER) 


Fig.  31. — The  three  states:  Solid,  liquid  and  gas.  The  cake  of  ice  represents  a  substance  in ' 
the  solid  state.  If  the  temperature  of  the  surrounding  air  be  above  the  freezing  point' 
(32®  Fahr.)  the  ice  will  gradually  melt,  that  is  to  say,  change  its  state  from  solid  to  liquid] 
this  process  being  known  as  fusion.  If  sufficient  heat  be  transferred  to  the  liquid,  it  will: 
boil,  that  is  to  say,  change  Us  state /row  liquid  to  gas,  this  process  being  known  as  vapori-  ; 
zation.^  Very  interesting  phenomena  take  place  during  these  changes,  which  are  ex- ^ 
plained  in  the  accompanying  text.  J 


Oues.     Under  what  conditions  does  steam  exist? 

Ans.     When    there    is    the    proper    relation    between    the! 


*NOTE. — ^A  term  sometimes,  though  ill  advisedly,  used  for  highly  superheated  steam  is^ 
gaseous  steam  or  steam  gas.  The  saving  in  the  water  consumption  of  a  steam  engine  due  to  \ 
superheating  the  steam  is  a  little  over  one  per  cent  for  each  ten  degrees  of  superheat.  i 


BASIC  PRINCIPLES 


25 


temperature  of  the  water  and  the  external  pressure.  For 
instance,  for  a  given  temperature  of  the  water  there  is  a  certain 
external  pressure  above  which  steam  will  not  form, 

Oues.     How  is  steam  produced? 

Ans.     By  heating  water  until  it  reaches  the  boiling  point. 


Fig,  32. — The  fusion  of  ice,  illustrating  the  work  done  when  the  pound  of  ice  at  32**  Fahr. 
is  melted  or  converted  into  water  at  the  same  temperature.  The  latent  heat  of  fusion  being 
143.57  heat  units,  and  since  one  heat  unit  is  equivalent  to  778  ft.  lbs.  the  work  done  during 
the  fusion  of  one  pound  of  ice  is  778X143.57=111,698  ft.  lbs.  This  is  approximately 
equivalent  to  the  work  done  when  a  hoisting  engine  hoists  2,000  lbs.  a  distance  of  55.8  ft. 
as  shown  in  the  illustration. 


What  an  Engineer  should  know  about  Steam. — As  has 

been  stated,  the  medium  which  transmits  heat  energy  to  the 
engine  to  be  transformed  into  mechanical  work  is  a  very  re- 
markable substance;  it  disobeys  the  general  law  of  expansion 
by  heating,  and,  can  exist  in  three  different  states,  that  is,  as 

1.  A  solid  (ice); 
^  2.  A  liquid  (water),  or 

3.  A  gas  (steam). 


26 


BASIC  PRINCIPLES 


THE      HEAT      AND      WORK      REQUIRED 

TO     MAKE     STEAM 
Stage  1  Stage  2  Stage  3  Stage  4 


^-■ 

Ui 

2 

X 

5 

o 

h 

o 

f. 

3 

o 

2 

2 

o 

or 

= 

c 

O 

o 

Q 

z 

o 

z 

z> 

r- 

3 

t- 

a 

< 

> 

> 

z 

-1 

o 

o 

o 

lO 

> 

lnTF 

llli 

/ 

\ 

m- 

^li 



5f  age  5 


S  cr  «n 
o.  «o  -I 


EI 


s 


i 


5  ?  a 


< 

Stag 

e(? 

I 

llllhlllll 

F'-'.;    >:.     "I 

> 

CO 

-v-:;.?£ 

o 

.■  -oi 

Ul 

■■■■■■■  -^^ 

a.    \- 

< 

-^ 

■;■■"■/ -2 

o   I* 

-.■  < 

H 

O   o 

± 

J  ^ 

w 

H  UI 

1^2 

Si 

be 

r  cv»: 

'^  z 

o 

■t- 

ifio 

tj     Uj 

■■.  •  •:  ■< 

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S2 

t>     3 

Q_: 

o   o 

>  > 

N 

i:! 

---1 



\^ 

tTN 

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T 

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t- 

Figs.  33  to  38. — From  ice  to  8tearn>  illustrating  the  six  stages  in  the  making  of  steam  trom  ^ 
ice  at  32°  Fahr.  i 


BASIC  PRINCIPLES 


27 


depending  upon  conditions  of  pressure  and  temperature.  These 
changes  are  shown  in  the  accompanying  series  of  diagrams, 
(figs.  33  to  38),  which  represent  the  several  stages  in  transforming 
a  pound  of  ice  at  32°  Fahr.  into  saturated  steam  at  212°,  the 
temperature  corresponding  to  atmospheric  pressure.  The 
engineer  should  make  a  careful  study  of  these  diagrams  and  the 
matter  following  to  properly  understand  the  nature  of  the  medium 
he  has  to  deal  with  in  the  operation  of  an  engine. 


NJON-CONDUCTING  VESSEL 


3  LBS  OF  WATER 


I  LB.  OF  ICE 

AT  32"  FAHR 

/ 


2  LBS.  OF  WATER 

AT  88° 

Figs.  39  to  41. — Experiment  illustrating  the  latent  heat  of  fusion.  It  requires  *144  heat  units 
to  "melt"  a  pound  of  ice  at  32°  Fahr.,  that  is,  to  convert  it  into  water  of  the  sarne  temperature. 
Accordingly,  if  a  pound  of  ice  (fig.  39)  be  placed  in  a  non-conducting  vessel  with  two  pounds 
of  v/ater  at  88"  Fahr.,  it  will  be  found  that  when  all  of  the  ice  has  been  melted  by  the 
transfer  of  heat  from  the  water  to  the  ice  the  temperature  of  the  mixture  (fig.  41)  of  melted 
ice  and  the  water  will  be  the  same  as  the  original  temperature  of  the  ice,  32°.  The  reason  for 
this  is  because  the  total  heat  above  32°  in  the  water  at  88°  was  the  same  as  the  latent 
heat  of  the  ice,  or  144  heat  units,  that  is  to  say,  the  total  heat  above  32°  in  the  water  was 
(88  X  2)  —  32  =  144  heat  units.  It  should  be  understood  that  the  term  non-con- 
ducting vessel  implies  one  in  which  allows  no  heat  to  pass  through  its  sides.  Such  a  vessel 
is  not  possible  to  construct,  but  by  covering  an  ordinary  vessel  all  over  with  a  thick  layer  of 
asbestos  very  little  heat  will  be  lost. 


It  will  be  noted  from  the  diagrams  that  the  stages  into  which 
the  process  of  transforming  ice  into  steam  by  heating  are 

1.  Fusion  of  the  ice  (at  32°  F.); 

2.  Contraction  of  the  water  (between  32°  and  39.1°); 

3.  Expansion  of  the  water  (between  39.1°  and  212°); 

*N0TE. — According  to  the  U.  S.  Bureau  of  Standards,  1915,  the  latent  heat  of  fusion  of 
ice  is  143.57  B.  t.  u.,  however  for  ordinary  calculations  the  value  144  is  conveniently  used. 


28 


BASIC  PRINCIPLES 


4.  Vaporization,  or  formation  of  steam  at  212°.  i 

During  the  process  two  changes  of  state  have  occurred:  ' 

1.  Solid  to  liquid  (ice  to  water)  at  freezing  point  32°  Fahr. ;, 

2.  Liquid  to  gas  (water  to  steam)  at  boiling  point  212°  Fahr.^n 

To  effect  these  two  changes  of  state,  a  considerable  amount  of  work  is* 
done,  especially  in  the  case  of  the  second  change  from  liquid  to  gas,  thev 
amounts  required  being  i 


Figs.  42  to  44, — The  bursting  of  pipes  during  freezing  weather,  illustrating  the  effect  of  pressure  j 
upon  the  freezing  point.  In  draining  pipes  exposed  to  prevent  freezing,  care  should  be  taken  ; 
to  remove  all  the  water  out  of  any  water  pockets  that  may  exist,  such  as  shown  in  fig.  42.  \ 
The  bursting  of  a  pipe  due  to  water  in  a  pocket  is  illustrated  in  figs.  43  and  44,  whicTi  show  < 
fig.  42  in  section.  Assuming  the  pocket  to  be  full  of  water  in  freezing  weather,  it  sometimes  \ 
happens  that  the  water  at  A  and  B,  will  freeze  before  it  does  at  C,  thus  forming  two  slugs  of  ] 
ice  enclosing  the  water  C.  When  C,  freezes,  there  being  no  room  for  expansion,  the  pipe 
bursts  as  indicated  at  D.  The  popular  impression  that  pipes  will  burst  at  or  very  little 
below  32°  Fahr.,  is  erroneous.  In  fact  the  enormous  pressure  required  to  burst  so  called  ; 
wrought  iron  pipe  is  not  generally  known,  nor  the  effect  of  the  pressure  on  the  freezing  point,  j 
For  instance,  the  average  bursting  pressure  of  one-half  inch  standard  pipe  is  14,000  lbs.,  or  \ 
911.5  atmospheres;  per  sq.  in.  and  since  the  freezing  point  is  lowered  .0133°  Fahr.  for  each  > 
additional  atmosphere,  the  freezing  point  required  to  burst  one-half  inch  pipe  is  32  —  (911.5  X  , 
.0133)  =20'"  Fahr.;  that  is  to  say,  it  would  require  a  temperature  of  20°  to  burst  a  one-half  i 
inch  pipe  of  average  strength  by  freezing.  ' 


1.  To  melt  the  ice 143.57  B.  t.  u. 

2.  To  change  the  water  at  212°  Fahr.  into  steam  of  the 

same  temperature 970.4    B.  t.  u. 


BASIC  PRINCIPLES 


29 


It  will  be  noted  from  these  two  items  that  it  takes  over  five  times  as 
much  heat  to  evaporate  water  at  212°  Fahr.  into  steam  of  the  same  tem- 
perature, as  it  does  to  heat  the  water  from  the  freezing  point  to  the  boiling 
point.  That  is  to  raise  the  temperature  of  the  water  from  the  freezing 
point  to  the  boiling  point  requires  212  —  32  =  180  B.  t.  u.,  and  from  item  2, 
which  represents  the  latent  heat  of  steam,  970.4  B.  t.  u.  are  required  to  evap- 
orate the  water  at  212°  into  steam  of  the  same  temperature.    From  which 

>0  / — A   ^ 


Figs.  45  to  47. — Experiment  illustrating  the  latent  heat  of  steam  or  the  considerable  amount 
of  heat  which  must  be  added  to  water  at  the  boiling  point  to  convert  it  into  steam  at  the  same 
temperature.  In  fig.  45,  suppose  the  glass  vessel  to  contain  one  pound  of  water  at  32°  Fahr., 
and  heat  be  transferred  to  it,  as  indicated  by  the  bunsen  burner,  at  such  rate  that  its 
temperature  is  raised  to  the  boiling  point  212°  in  five  minutes.  In  this  time  the  water  has 
received  212  —  32  =  180  heat  units.  Now,  if  the  heat  supply  be  continued  at  the  same  rate, 
it  will  require  (since  the  latent  heat  of  steam  at  atmospheric  pressure  is  970.4  heat  units) 
970.4  -J- 180  =5.39  times  as  long,  or  5.39  X5  =26.95  minutes  to  convert  the  pound  of  water  at 
212°  (fig.  46)  into  steam  at  the  same  temperature  as  indicated  by  the  empty  beaker  in  fig. 
47.  That  is  to  say,  it  takes  over  five  times  as  much  heat  to  convert  water  at  212°  into  steam 
at  the  same  temperature  as  it  does  to  raise  the  same  amount  of  water  from  the  freezing  point 
32°  to  212°.  This  experiment  can  be  easily  performed  with  water  at  ordinary  temperature 
say  60°.  In  this  case,  if  it  take  five  minutes  to  raise  its  temperature  to  212°,  it  would  require 
970.4^(212  — 60)  =6.38  times  as  long  or  6.38X5=31.9  minutes  to  evaporate  the  water 
at  212°.^  It  is  thus  seen  that  the  latent  heat  is  the  big  item  in  steam  making.  In  the  well 
known  "naphtha  launch"  and  "alco-vapor  launch,"  naphtha,  and  alcohol  were  used  respectively 
in  the  boilers  in  the  place  of  water  because  of  the  excessive  latent  heat  of  the  latter.  This 
with  a  given  heating  surface  or  weight  (an  important  factor  in  marine  construction)  more 
power  could  be  developed  with  the  above  mentioned  liquids  than  with  water,  because  of 
their  relative  low  latent  heat  of  evaporation.  For  instance,  for  alcohol  the  latent  heat  is 
364.3  heat  units  or  only  a  little  over  one- third  of  that  of  water.  Operators  of  alco-vapor 
launches  who  have  tried  using  water  in  the  boiler  can  appreciate  the  considerable  difference 
in  the  results  obtained.  From  experiments  made  by  the  Gas  Engine  and  Power  Co.,  builders 
of  the  naphtha  launches,  it  was  claimed  that  the  power  obtained  on  the  brake  was  in  the  ratio 
of  about  5  to  9  for  steam  and  naphtha,  that  is,  the  same  quantity  of  heat  was  turned  into 
nearly  twice  as  much  work  by  the  expansion  of  naphtha  vapor  as  by  the  expansion  of  steam 
under  the  same  conditions.  Some  of  the  results  obtained  during  the  tests  were:  1,  with 
steam,  mean  pressure  37.99  lbs.,  r.p.m.,  312.6;  2,  with  naphtha,  mean  pressure  55.8, 
r.p.m..  552.2. 


30 


BASIC  PRINCIPLES 


it  requires  970.4 -^  180  =  5.39  times  as  much  heat  to  evaporate  the  water 
as  it  does  to  heat  the  water  between  the  Hmits  given.  This  relation  can  be 
approximately  determined  by  the  interesting  experiment  shown  in  figs.  45 
to  47.  The  heat  which  must  be  supplied  during  the  process  of  evaporation 
has  been  expended  in  two  ways. 

1 .  In  overcoming  the  molecular  resistance  of  the  medium  H2O  in  changing 
its  state  from  a  liquid  to  a  gas; 

2.  In  making  room  for  itself  against  the  pressure  of  the  atmosphere,  that 
is,  doing  external  work.    These  two  amounts  of  heat  are  called  respectively 

1.  The  internal  latent  heat; 

2.  The  external  latent  heaty 
^n        both  making  up  the  latent  heat  of  steam. 


Fig.  48. — ^The  work  done  in  the  formation  of  steam  from  water  at  32°  P'ahr. ,  In  converting 
one  pound  of  water  at  32°  into  steam  at  212°,  180  heat  units  are  required  to  raise  the  tem- 
perature of  the  water  to  212°;  897.51  heat  units  are  absorbed  by  the  water  at  212°  before 
a  change  of  state  takes  place,  and  72.89  heat  units  are  required  for  the  work  to  be  done  on 
the  atmosphere  to  make  room  for  the  steam.    These  three  items  are  known  respectively  as : 

1,  the  sensible  heat;  2,  the  internal  latent  heat,  and  3,  the  external  latent  heat.  The 
mechanical  equivalent  of  one  heat  unit  being  777.52  ft.  lbs.,  the  respective  amounts  of  work 
corresponding  to  the  sensible,  internal,  and  external  latent  heats  are  139,954  ft.  lbs.,  . 
097,832  ft.  lbs.,  and  56,674  ft.  lbs.  To  grasp  the  significance  of  this,  consider  a  locomotive 
boiler  weighing,  say  50,000  lbs.  being  lifted  by  a  crane.  The  work  done  in  lifting  the  boiler 
is  equal  to  its  weight  in  pounds  multiplied  by  the  distance  raised  in  feet.  Accordingly,  for 
item  1,  the  work  done  is  equivalent  to  raising  the  boiler  139,954  4-50,000  =2.8  ft.;  for  item 

2,  equivalent  to  697,832-7-50,000  =  13.96  ft.,  and  for  item  3,  equivalent  to  56,674-5-50,000  = 
1.13  ft.  Also  the  total  work  done  in  changing  a  pound  of  water  at  32°  into  steam  at  212°, 
or  the  sum  of  the  three  items  is  equivalent  to  raising  the  boiler  2. 8 -f  1 3. 96 -f  1.03  =17.89  ft. 


BASIC  PRINCIPLES  31 


The  author  does  not  agree  with  the  generally  accepted  calculation  for 
the  external  latent  heat,  or  external  work  of  vaporization  and  holds  that 
it  is  wrong  in  principle.  The  common  method  of  calculating  this  work  is 
based  on  the  assumption  that  the  amount  of  atmosphere  displaced  per 
pound  of  steam,  is  equal  to  the  volume  of  one  pound  of  saturated  steam 
at  the  pressure  under  which  it  is  formed;  it  is  just  this  point  wherein  the 
error  lies,  as  will  now  be  shown.  The  volume  of  one  pound  of  water  at 
212°  atmospheric  pressure,  is  28.88  cu.  ins.  Now,  if  this  water  be  placed 
in  a  long  cylinder,  having  a  cross  sectional  area  of  144  sq.  ins.  it  will  occupy 
a  depth  of  .0167  ft. 

If  a  piston  (assumed  to  have  no  weight  and  to  move  without  friction)  be 
placed  on  top  of  the  water  as  in  stage  4  (fig.  36),  and  heat  applied,  vapor- 
ization will  begin,  and  when  all  the  water  has  been  changed  into  saturated 
steam,  the  volume  has  increased  to  26.79  cu.  ft.,  as  in  stage  6,  (fig.  38),  that 
is,  the  volume  of  one  pound  of  saturated  steam  at  atmospheric  pressure  is 
26.79  cu.  ft. 

Since  the  area  of  the  piston  is  1  sq.  ft.,  the  linear  distance  from  the 
bottom  of  the  cylinder  to  the  piston  is  26.79  ft.,  but  the  piston  has  not 
moved  this  distance.     The  initial  position  of  the  piston  being  .0167  ft. 
above  the  bottom  of  the  cylinder,  its  actual  movement  is 
26.79  —  .0167=26.7733  ft. 

Accordingly,  the  work  done  by  the  steam  in  moving  the  piston  against 
the  pressure  of  the  atmosphere  to  make  room  for  itself  or 

external  work  —  area  piston  X  pressure  of  atmosphere  X  movement  of  piston 
=  144  sq.  ins.  X     14.7  lbs.  per  sq.  ins.     X        26.7733  ft. 

=  56,673.72  ft.  lbs. 
The  erroneous  method  of  making  this  calculation  is  to  consider  the 
movement  of  the  piston  equal  to  the  distance  between  the  bottom  of  the 
cylinder  and  the  piston,  or  26.79  ft.,  which  would  give  for  the  external 
Work 

144X14.7X26.79  =56,709.07  ft.  lbs. 

being  in  excess  of  the  true  amount  by 

56,709.07  —  56,673.72  =  35.35  ft.  lbs. 
or 

.0167  ft.  X 144  sq.  ins.  X  14.7  =  35.35  ft.  lbs. 

Motion  is  purely  a  relative  matter,  and  accordingly  something  must 
be  regarded  as  being  stationary  as  a  basis  for  defining  motion;  hence  the 
question : 

75  the  movement  of  the  piston  in  stage  6  (fig.  38)  to  he  referred  to  a  station- 
ary  water  level  or  to  a  receding  water  level? 

The  author  holds  that  the  movement  of  the  piston  referred  to  a  stationary 
water  level  gives  the  true  displacement  of  the  air  and  is  accordingly  the 
proper  basis  for  calculating  the  external  work.  It  must  be  evident  that 
since  the  water  already  existed  at  the  beginning  of  vaporization,  the 
atmosphere  was  already  displaced  to  the  extent  of  the  volume  occupied 


32 


BASIC  PRINCIPLES 


S  Of: 


g   §•  c 


S«     c    Q    °* 


Co 


«5, 


^"F 


^     15! 


■  (^  X 


is  ^S. 


12    t  -5    §  -^ 


1  ?s 


CO    (N«^ 


e 

tg 


^ 


BASIC  PRINCIPLES 


33 


by  the  water,  and  therefore  this  displacement  must  not  be  considered  as 
contributing  to  the  external  work  done  by  the  steam  during  its  formation. 
The  amount  of  error  (35.35  ft.  lbs.)  of  the  common  calculation,  though  very 
small,  is  an  appreciable  amount;  its  equivalent  in  heat  units  is 

35.35 -^ 777.52  =  .0455  B.  t.  u. 


The  thermal  equivalent  of  the  external  work  is 

56,673.72-^777.52=72.89  B.  t.  u. 


GAUGE 
PRESSURE 


Condensation  of 
Steam,  —r  When  the 
temperature  of  steam 
becomes  less  than  that 
corresponding  to  its 
pressure y  condensa- 
tion takes  place,  that 
is,  it  ceases  to  exist  as 
steam  and  becomes 
water. 


Fig.  49. — The  generation  of  steam  at  pressures  above  the  atmosphere.  If  a  ring  B,  be  riveted 
in  a  cyUnder  to  limit  the  movement  of  a  piston  resting,  at  the  beginning  of  the  experiment,  on 
top  of  a  small  quantity  of  water  (as  indicated  by  dotted  lines  A,  and  heat  be  applied,  the 
piston  (assumed  to  have  no  weight)  will  rise  as  steam  is  formed  at  atmospheric  pressure  until 
it  comes  in  contact  with  the  ring  B,  Additional  heat  will  cause  the  pressure  of  the  steam 
to  increase  in  a  definite  rate  corresponding  to  the  temperature  until  all  the  water  is  evaporated, 
the  cylinder  being  now  filled  with  saturated  steam.  The  pressure  of  this  saturated  steam  will 
depend  on  the  relation  between  its  volume  and  the  volume  of  the  water  from  which  it  was 
generated.  If  more  heat  be  now  added,  the  temperature  of  the  steam  will  increase  above 
that  due  to  its  pressure,  and  the  steam  becomes  superheated.  Removing  the  heat  supply, 
the  temperature  of  the  gas  will  gradually  diminish,  and  it  loses  its  superheat  and  returns  to 
the  saturated  condition,  at  which  point  condensation  begins,  the  pressure  and  temperature 
during  these  changes  gradually  falling.  Condensation  continuing  until  all  the  steam  has 
condensed,  the  piston  returning  to  its  initial  position  A.  If*  during  the  cooling  process,  the 
piston  be  fastened  at  the  ring  B,  the  pressure  of  the  steam  will  become  less  than  the  atmos- 
pheric pressure  outside  when  the  temperature  falls  below  212*  Fahr.,  forming  a  so  called 
vacuum.  The  degree  of  vaauum  now  increases,  or  in  other  words,  the  pressure  under  the 
cylinder  or  absolute  pressure  becomes  less  and  less  until,  when  all  the  steam  is  condensed, 
it  becomes  approximately  zero,  or  14.72  lbs.  lower  than  the  pressure  of  the  atmosphere  or 
gauge  pressure,  (assuming  the  barometer  reads  30  inches).  The  pressure  remains  a  little 
above  zero  because  of  the  small  percentage  of  air  originally  contained  in  the  water,  which 
does  not  recombine  with  it  when  the  steam  condenses,  that  is,  a  perfect  vacuum  is  not  formed 
because  of  this  air,  necessitating,  in  the  case  of  condensing  engines,  an  air  or  so  called  vacuum 
pump. 


34 


BASIC  PRINCIPLES 


Thus  in  fig.  50,  if  cold  water  be  poured  on  the  inverted  flask,  containing 
steam  and  water,  the  steam  will  be  cooled  below  its  temperature  correspond- 
ing to  its  pressure  (as  given  in  the  steam  table)  and  some  of  it  will  condense. 
This  will  cause  a  reduction  of  pressure  because  the  volume  of  steam  is 
greatly  diminished  after  condensation.*  On  account  of  the  reduction  in 
pressure,  the  water  will  again  boil  vigorously  until  enough  steam  has  been 
formed  to  increase  the  pressure  to  correspond  with  the  boiling  point. 


COOLING 
WATER 


VACUUM  &>\U6E: 


Fig.  50. — Lowering  the  boiling  point  by  diminishing  the  pressure.  Fill  a  round  bottomed  flask 
with  water  and  boil.  After  it  has  boiled  some  time,  until  the  air  has  been  drawn  out  of  the 
flask  by  the  steam,  insert  a  rubber  stopper,  having  fitted  to  it  a  connection  leading  to  a 
vacuum  gauge  and  invert  the  flask  as  shown.  The  vacuum  gauge  will  now  read  zero.  Now, 
ii  some  cold  water  be  poured  over  the  flask,  the  temperature  will  fall  rapidly  and  some  of  the 
steam  will  condense,  thus  lowering  the  pressure  within  the  flask,  that  is,  the  vacuum  gauge 
will  read  5  or  10  inches  indicating  a  vacuum.  The  reduced  pressure  disturbs  the  equilibrium 
between  pressure  and  temperature  and  the  water  will  boil  until  equilibrium  is  again  restored. 
The  operation  may  be  repeated  several  times  without  reheating,  the  pressure  gradually 
falling  each  time.  At  the  city  of  Quito,  Ecuador,  water  boils  at  194°  Fahr.,  and  on  the  top 
of  Mt.  Blanc  at  183°.  Again,  in  a  steam  boiler  in  which  the  pressure  is  200  lbs.,  the  boiling 
point  is  387.7°. 


*NOTE.— It  should  be  remembered  that  1  cu.  ft.  of  steam  at  atmospheric  pressure  is 
reduced  in  volume  after  condensation  to  approximately  1  cu.  in. 


BASIC  PRINCIPLES  35 

A  second  application  of  cold  water  will  again  cause  the  water  to  boil, 
pthe  result  being  the  same  so  long  as  the  water  in  the  flask  is  at  a  higher 
temperature  than  the  water  applied  outside. 

The  greater  the  difference  in  temperature,  the  more  vigorous  will  the 
water  boil.  This  illustrates  an  important  effect  in  the  behavior  of  steam 
in  a  steam  engine,  namely,  re-evaporation  which  will  be  later  explained. 

Ones.  If  a  closed  flask  containing  steam  and  water  be 
allowed  to  stand  for  a  length  of  time,  what  happens? 

Ans.  The  atmosphere  being  at  a  lower  temperature  than 
that  inside  the  flask,  will  abstract  heat  from  the  steam  and  water, 
but  the  heat  will  leave  the  steam  quicker  than  the  water.  The  result 
is  a  continuous  condensation  of  the  steam  and  re-evaporation 
of  the  water,  during  which  process  the  temperature  of  the  whole 
mass  and  the  boiling  point  is  gradually  lowered  until  the  tem- 
perature inside  of  the  flask  is  the  same  as  that  outside.  This 
process  is  accompanied  by  a  gradual  decrease  in  pressure. 

Oues.    Why  does  the  pressure  fall? 

Ans.     Because  the  temperature  falls. 

There  is  a  fixed  pressure  for  each  degree  of  temperature  of  the  water 
as  tabulated  in  the  steam  tables. 

Oues.  Can  this  pressure  be  reduced  to  zero  by  reducing 
the  temperature  of  the  water? 

Ans.  It  could,  if  the  mass  could  be  cooled  to  459.4°  below 
zero  Fahr.*,  but  at  ordinary  temperatures  the  pressure  could 
not  be  reduced  to  zero.  Water  contains  a  small  amount  of  air 
which  it  gives  up  when  evaporated;  this  of  itself  would  prevent 
the  pressure  falling  to  zero,  if  all  the  steam  were  condensed. 
If  the  contents  of  the  flask  be  cooled  to  80°  there  would  be 
inside  the  flask  a  pressure  of  one-half  pound  per  square  inch, 

*NOTE. — 459.6°  below  zero  Fahr.,  as  previously  explained,  is  a  point  called  the  absolute 
zero.  A  perfect  gas  contracts  in  volume  a  definite  amount  for  each  degree  in  temperature  it 
is  cooled.  The  absolute  zero  then  is  the  point  to  which  a  perfect  gas  must  be  cooled  to  reduce 
its  volume  to  nothing. 


36 


BASIC  PRINCIPLES 


if  the  water  be  cooled  to  32°,  the  pressure  would  be  .089  pounds,  j 
There  is  then  always  some  pressure  inside  the  flask,  the  intensity ; 
of  which  depends  upon  the  temperature  of  the  water.  j 

Oues.     How  was  this  principle  first  made  use  of? 

Ans.     The  early  engineers  discovered  that  by  condensation; 
the  pressure  of  the  atmosphere  is  made  available  for  doing  work.  ; 

Fig.  51. — Newcomen's  atmospheric 
engine.      The    parts    are:     A, 

furnace;  B,  boiler;  C,  valve;  D,  ' 
cylinder;  E,  piston;  F,  piston  rod;  ' 
G,  walking  beam;  H,  pump  rod; 
J,  pump  cylinder;  K,  pump; 
barrel;  L,  injection  water  pump;  : 
M,  injection  water  pipe;  N,  ' 
injection  valve;  O,  water  supply 
cock  to  seal  piston;  P,  air  check 
or  snifting  valve;  Q,  injection 
water  discharge  pipe;  R,  hot 
well.  In  Newcomen's  engine,  the  '• 
piston  was  attached  by  rod  and  i 
chain  to  one  end  of  the  walking-  ' 
beam,  and  the  pump  rod  to  the  1 
other  end.  The  pump  rod  was  \ 
heavy  enough  to  sink  it  in  the  j 
barrel  and  raise  the  steam  piston,  ] 
or  else  a  weight  was  added.  The  I 
periphery  of  the  piston  was  | 
covered  with  leather  and  kept  i 
air  tight  by  water  above  it,  ad-  ' 
mitted  through  cock  O.  The  ! 
cylinder  D,  was  placed  above  the  ! 
boiler  B,  and  steam  was  admitted  [ 
to  it  through  the  cock  C,  which  ' 
was  tended  by  hand,  the  strokes  i 
being  slow.  At  starting,  the  air  from  the  cylinder,  displaced  by  the  steam,  passed  out  through  ■ 
the  pipe  which  proceeds  from  the  bottom  of  the  cylinder,  and  issued  at  the  valve  P,  which  | 
opened  upwardly.  This  is  the  blow  valve  or  snifting  valve  of  the  engine.  The  cock  C,  being  then 
closed,  shuts  off  the  steam,  and  the  cock  N,  being  opened,  allows  injection  water  to  enter  the  ' 
cylinder  from  injection  pump  K,  through  pipe  M.  The  water,  being  condensed  into  about  | 
Vi728  of  its  bulk,  formed  a  nearly  perfect  vacuum,  and  the  atmospheric  pressure  of  14.7  i 
pounds  to  the  square  inch  bearing  upon  the  piston  depressed  the  latter,  and  consequently  j 
raised  the  pump  rod,  the  weight  (if  there  be  any),  and  the  load  of  water.  The  downward  ■ 
stroke  only  of  the  piston  was  used  effectively.  The  water  of  injection  and  condensation  i 
passed  by  the  pipe  Q,  leading  from  the  bottom  of  the  cylinder  to  the  hot  well  R,  issuing  through  ) 
a  check  valve,  and  was  used  to  feed  the  boiler.  It  wiK  be  observed  that  the  piston  and  \ 
pump  rod  are  merely  suspended  by  chains;  the  action  of  each  is  to  pull,  not  push,  and  a  ' 
stiff  connection  was  not  necessary.  At  first  Newcomen  adopted  Savery's  plan  of  external  I 
condensation,  but  a  faulty  cylinder  having  admitted  water  internally,  the  condensation  i 
was  more  rapid  with  increased  effect  from  the  engine.  i 


NOTE. — The  taps  which  answered  as  valves  in  the  Newcomen  engine  required  the  most 
unremitting  attention  of  the  person  in  charge,  to  introduce  steam  into  the  cylinder  to  lift  the 
piston,  or  the  shower  of  cold  wa.ter  which  was  to  condense  the  steam  and  cause  the  depression 
of  the  piston  by  the  atmospheric  pressure  above  it.  A.  Cornish  boy,  named  Potter,  in  order 
to  have  some  time  for  play  conceived  and  put  in  execution  the  idea  of  connecting  the  beam  to 
the  handle  of  the  taps,  so  as  to  work  them  automatically.  ^  Hence  the  valve  motion.  For  the 
first  time,  the  engine  worked  by  itself.  With  the  exception  of  Smeaton's  improvements  in 
details,  the  Newcornen  engine  remained  in  the  state  to  which  its  inventor  had  brought  it,  from 
1710  to  1764,  about  which  time  Watt  appeared. 


BASIC  PRINCIPLES 


37 


Ones.     What  is  the  chief  objection  to  this  engine?  \ 

Ans.     It  was  discovered  by  James  Watt  in  1763  that  there  | 

was  a  large  waste  of  steam  in  the  cylinder  owing  to  condensation  \ 

of  the  steam  through  contact  with  the  cold  wet  cylinder  walls.  | 

Ones.     How  did  Watt  overcome  this  defect? 


CIRCULATING 
WATER 


-^"4       5TE.A»^ 


WE.LL 


Fig.  52. — The  condensation  of  steam.  If  water  be  boiled  in  a  flask  A,  and  the  steam  thus 
produced  led  off  through  pipe  C,  having  a  coiled  section  surrounded  by  cold  water,  it  will 
here  be  cooled  below  the  boiling  point  and  will  therefore  condense,  the  condensate  passing 
out  into  the  receptacle  B,  as  water.  The  cooling  or  "circulating"  water  enters  the  condenser 
at  the  lowest  point  D,  and  leaving  at  the  highest  point  E. 


Ans.  He  invented  a  separate  chamber  in  which  the  con- 
densation took  place.  The  steam  was  passed  from  the  cylinder 
into  this  chamber,  called  the  condenser  where  it  was  condensed 
by  contact  with  cold  water  without  the  need  of  cooling  the 
cylinder  itself. 


38  BASIC  PRINCIPLES 


The  elementary  condenser  shown  in  fig.  52  illustrates  the  method  of 
condensing  steam  after  it  leaves  the  engine  cylinder  by  bringing  it  in 
contact  with  a  cold  metallic  surface.  Such  method  is  called  surface  con- 
densation, and  the  apparatus,  a  surface  condenser. 

In  the  figure,  the  flask  A,  placed  over  a  Bunsen  burner,  is  fitted  with  a 
rubber  cork  and  tube  C,  part  of  which  is  coiled  and  surrounded  by  flowing 
cold  water.  A  glass  vessel  or  beaker  B,  is  placed  under  the  end  of  the  coil 
as  shown. 

When  water  is  boiled  in  A,  the  steam  thus  formed  will  pass  off  through  C, 
and  in  traversing  the  coiled  part  it  is  cooled  below  the  temperature  cor- 
responding to  its  pressure  and  condenses.  The  water  thus  formed  or  con- 
densate passes  in  drops  from  the  end  of  the  tube  C,  into  the  vessel  B.  When 
all  the  water  has  been  evaporated  from  A,  it  will  be  found  that  the  same 
weight  of  water  originally  placed  in  A,  has  been  deposited  in  B. 

The  condensation  of  steam  may  also  be  illustrated  by  fig.  49,  assuming 
the  supply  of  heat  to  be  removed. 

If  the  piston  be  pushed  downward,  the  tendency  will  be  to  increase  both 
the  pressure  and  temperature  of  the  steam.  However,  if  there  be  any 
increase  in  the  temperature  of  the  steam  it  is  immediately  cooled  by  the 
water  which  causes  condensation  and  keeps  the  pressure  constant.  In 
fact  all  the  steam  could  be  condensed  by  pushing  the  piston  downward 
until  it  rested  on  the  surface  of  the  water. 

If  the  piston  be  now  returned  to  its  original  position,  steam  will  im- 
mediately form  and  fill  the  space,  the  pressure  remaining  constant.  The 
reason  for  this  is  that  unless  the  empty  space  formed  by  the  receding  piston 
be  immediately  filled,  the  pressure  will  fall,  thus  exposing  the  water  which 
is  at  212°  to  a  pressure  lower  than  the  boiling  point.  Under  these  con- 
ditions the  water  boils  until  the  empty  space  is  filled  with  steam  of  a 
density  corresponding  to  the  boiHng  point,  thus  preserving  a  constant 
pressure. 

How  to  Use  the  Steam  Table. — The  various  properties  of 
saturated  steam  are  usually  presented  in  tabulated  form  for 
convenience  in  making  calculations.  The  values  of  the  properties 
of  steam  here  given  are  condensed  from  Marks  and  Davis  steam 
tables  which  are  now  (1917)  generally  accepted  as  the  standard, 
and  are  the  most  accurate  that  have  yet  been  published. 

In  the  first  column  is  given  the  gauge  pressure,  and  in  the  second,  the 
absolute  pressure.  The  second  column,  then,  is  made  up  by  adding  14.7 
lbs.  to  the  pressures  given  in  the  first  column.  Before  using  a  steam  table, 
the  difference  between  gauge  and  absolute  pressure  should  be  thoroughly 
understood. 


BASIC  PRINCIPLES  39 


The  third  column  gives  the  temperature  in  degrees  Fahrenheit,  beginning 
with  the  freezing  point  32°,  which  for  convenience  is  taken  as  the  temperature 
of  no  heat. 

Column  four  gives  the  total  heat  above  32°  in  each  pound  of  water  at 
the  different  pressures ;  similarly  in  column  five  is  given  the  total  heat  above 
32°  for  each  pound  weight  of  steam. 

The  latent  heat  in  the  next  column  is  clearly  the  difference  between 
the  heat  in  the  steam  and  the  heat  in  the  water,  or  column  5-^column  4. 

The  relative  volume  of  the  steam  is  given  in  column  seven ;  for  instance, 
one  cubic  foot  of  water  at  212°  will  occupy  26.79  cu.  ft.  when  evaporated 
into  steam  at  the  same  temperature. 

Column  eight  gives  the  weight  per  cu.  ft.,  and  the  last  two  columns  the 
entropy  values. 

The  following  examples  illustrate  how  to  use  the  steam  table: 

Example. — How  many  heat  units  are  saved  in  heating  25  lbs.  of  feed 
water  from  90  to  202°? 

In  column  4,  total  heat  in  the  water  at  201.96°  =  169.9 
In  column  4,  total  heat  in  the  water  at  90°  =  58.0 
Heat  units  saved  per  lb.  of  feed  water  =111.9 

Total  heat  units  saved  =  111.9X25  =2,797.5 

Example. — What  is  the  weight  of  20  cu.  ft.  of  steam  at  150  lbs.  absolute 
pressure? 

The  weight  of  1  cu.  ft.  steam  at  150  lbs.  abs.  is  given  in  column  9  at 
.332  1b.    Twenty  cu.  ft.  then  will  weigh:   .332X20  =  6.64  lbs. 

Example. — How  much  more  heat  is  required  to  generate  26  lbs.  of  steam 
at  150  lbs.  abs.,  than  at  90  lbs.  abs. 

In  column  5  total  heat  in  steam  at  150  lbs.  abs.  =1,193.4 
In  column  5  total  heat  in  steam  at  90  lbs.  abs.  =  1,184.4 
Excess  heat  required  per  pound  (weight)  =       ,9     B.  t.  u. 

Total  for  26  lbs.  =9X26=23.4  B.  t.  u. 

Example. — How  much  heat  is  absorbed  by  the  cooling  water,  if  a  con- 
densing engine  exhaust  17  lbs.  of  steam  per  hour  at  a  terminal  pressure 
of  18  lbs.  absolute  into  a  28  inch  vacuum. 

In  column  5,  total  heat  in  the  steam  at  18  lbs.  abs.        =  1,154.20 
In  column  4,  total  heat  in  the  water  with  28"  vacuum  =      67.97 
Heat  to  be  absorbed  per  lb.  of  steam .    .......    =1,086.23 

Total  heat  absorbed  by  the  cooling  water  per  hour 


1,086.23X17  =  18,465.9  B.  t.  u. 


40 


BASIC  PRINCIPLES 


Properties  of  Saturated  Steam 

Condensed  from  Marks  and  Davis'  Steam  Tables  and  Diagrams,   1909, 
permission  of  the  publishers,  Longmans,  Green  &  Co. 


*o 

< 

as  a 

Total  Heat 
above  32°  F 

"1 

IT 
3« 

.9 
^  1 

> 

if 

Sea 

O 
|l 

i 

11 

If 

> 
1^ 

29.74 

0.0886 

32 

0.00 

1073.4 

1073.4 

3294 

0.000304 

0.0000 

2.1832 

29.67 

0.1217 

40 

8.05 

1076.9 

1068.9 

2438 

0.000410 

0.0162 

2.1394 

29.56 

0.1780 

50 

18.08 

1081.4 

1063.3 

1702 

0.000587 

0.0361 

2.0865 

29.40 

0.2562 

60 

28.08 

1085.9 

1057.8 

1208 

0.000828 

0.0555 

2.0358 

29.18 

0.3626 

70 

38.06 

1090.3 

1052.3 

871 

0.001148 

0.0745 

1.9868 

28.89 

0.505 

80 

48.03 

1094.8 

1046.7 

636.8 

0.001570 

0.0932 

1.9398 

28.50 

0.696 

90 

58.00 

1099.2 

1041.2 

469.3 

0.002131 

0.1114 

1.8944 

28.00 

0.946 

100 

67.97 

1103.6 

1035.6 

350.8 

0.002851 

0.1295 

1.8505 

27.88 

1 

101.83 

69.8 

1104.4 

1034.6 

333.0 

0.00300 

0.1327 

1.8427 

25.85 

2 

126.15 

94.0 

1115.0 

1021.0 

173.5 

0.00576 

0.1749 

1.7431 

23.81 

3 

141.52 

109.4 

1121.6 

1012.3 

118.5 

0.00845 

0.2008 

1.6840. 

21.78 

4 

153.01 

120.9 

1126.5 

1005.7 

90.5 

0.01107 

0.2198 

1.6416 

19.74 

5 

162.28 

130.1 

1130.5 

1000.3 

73.33 

0.01364 

0.2348 

1.6084 

17.70 

6 

170.06 

137.9 

1133.7 

995.8 

61.89 

0.01616 

0.2471 

1.5814 

15.67 

7 

176.85 

144.7 

1136.5 

991.8 

53.56 

0.01867 

0.2579 

1.5582 

13.63 

8 

182.86 

150.8 

1139.0 

988.2 

47.27 

0.02115 

0.2673 

1.5380 

11.60 

9 

188.27 

156.2 

1141.1 

985.0 

42.36 

0.02361 

0.2756 

1.5202 

9.56 

10 

193.22 

161.1 

1143.1 

982.0 

38.38 

0.02606 

0.2832 

1.5042 

7.52 

11 

197.75 

165.7 

1144.9 

979.2 

35.10 

0.02849 

0.2902 

1.4895 

5.49 

12 

201.96 

169.9 

1146.5 

976.6 

32.36 

0.03090 

0.2967 

1.4760 

3.45 

13 

205.87 

173.8 

1148.0 

974.2 

30.03 

0.03330 

0.3025 

1.4639 

1.42 

lbs. 

gauge 

14 

209.55 

177.5 

1149.4 

971.9 

28.02 

0.03569 

0:3081 

1.4523 

14.70 

212 

180.0 

1150.4 

970.4 

26.79 

0.03732 

0.3118 

1.4447 

0.3 

15 

213.0 

181.0 

1150.7 

969.7 

26.27 

0.03806 

0.3133 

1.4416 

1.3 

16 

216.3 

184.4 

1152.0 

967.6 

24.79 

0.04042 

0.3183 

1.4311 

2.3 

17 

219.4 

187.5 

1153.1 

965.6 

23.38 

0.04277 

0.3229 

1.4215 

3.3 

18 

222.4 

190.5 

1154.2 

963.7 

22.16 

0.04512 

0.3273 

1.4127 

4.3 

19 

225.2 

193.4 

1155.2 

961.8 

21.07 

0.04746 

0.3315 

1.4045 

5.3 

20 

228.0 

196.1 

1156.2 

960.0 

20.08 

0.04980 

0.3355 

1.3965 

6.3 

21 

230.6 

198.8 

1157.1 

958.3 

19.18 

0.05213 

0.3393 

1.3887 

7.3 

22 

233.1 

201.3 

1158.0 

956.7 

18.37 

0.05445 

0.3430 

1.3811 

8.3 

23 

235.5 

203.8 

1158.8 

955.1 

17.62 

0.05676 

0.3465 

1.3739 

9.3 

24 

237.8 

206.1 

1159.6 

953.5 

16.93 

0.05907 

0.3499 

1.3670 

10.3 

25 

240.1 

208.4 

1160.4 

952.0 

16.30 

0.0614 

0.3532 

1.3604 

11.3 

26 

242.2 

210.6 

1161.2 

950.6 

15.72 

0.0636 

0.3564 

1.3542 

12.3 

27 

244.4 

212.7 

1161.9 

949.2 

15.18 

0.0659 

0.3594 

1.3483 

BASIC  PRINCIPLES 


41 


Properties  of   Saturated  Steam — Continued 


i 

g_d 

iSg- 

©.-fe 

si 

1^ 

<     ■ 

H 

Total  Heat 
above  32°  F 


II -s 


^ 


E  -a 


T-l-O 


28 

246.4 

29 

248.4 

30 

250.3 

31 

252.2 

32 

254.1 

33 

255.8 

34 

257.6 

35 

259.3 

36 

261.0 

37 

262.6 

38 

264.2 

39 

265.8 

40 

267.3 

41 

268.7 

42 

270.2 

43 

271.7 

44 

273.1 

45 

274.5 

46 

275.8 

47 

277.2 

48 

278.5 

49 

279.8 

50 

281.0 

51 

282.3 

52 

283.5 

53 

284.7 

54 

285.9 

55 

287.1 

56 

288.2 

57 

289.4 

58 

290.5 

59 

291.6 

60 

292.7 

61 

293.8 

62 

294.9 

63 

295.9 

64 

297.0 

65 

298.0 

66 

299.0 

67 

300.0 

214.8 
216.8 
218.8 
220.7 
222.6 
224.4 
226.2 
227.9 
229.6 
231.3 
232.9 
234.5 
236.1 
237.6 
239.1 
240.5 
242.0 
243.4 
244.8 
246.1 
247.5 
248.8 
250.1 
251.4 
252.6 
253.9 
255.1 
256.3 
257.5 
258.7 
259.8 
261.0 
262.1 
263.2 
264.3 
265.4 
266.4 
267.5 
268.5 
269.6 


1162.6 
1163.2 
1163.9 
1164.0 
1165.1 
1165.7 
1166.3 
1166.8 
1167.3 
1167.8 
1168.4 
1168.9 
1169.4 
1169.8 
1170.3 
1170.7 
1171.2 
1171.6 
1172.0 
1172.4 
1172.8 
1173.2 
1173.6 
1174.0 
1174.3 
1174.7 
1175.0 
1175.4 
1175.7 
1176.0 
1176.4 
1176.7 
1177.0 
1177.3 
1177.6 
1177.9 
1178.2 
1178.5 
1178.8 
1179.0 


947.8 
946.4 
945.1 
943.8 
942.5 
941.3 
940.1 
938.9 
937.7 
936.6 


935 

934 

933 

932 

931 

930 

929 

928 

927.2 

926.3 

925.3 

924.4 

923.5 

922.6 

921.7 

920.8 

919.9 

919.0 

918.2 

917.4 

916.5 

915.7 

914.9 

914.1 

913.3 

912.5 

911.8 

911.0 

910.2 

909.5 


14.67 

14.19 

13.74 

13.32 

12.93 

12.57 

12.22 

11.89 

11.58 

11.29 

11.01 

10.74 

10.49 

10.25 

10.02 

9.80 

9.59 

9.39 

9.20 

9.02 

8.84 

8.67 

8.51 

8.35 

8.20 

8.05 

7.91 

7.78 

7.65 

7.52 

7.40 

7.28 

7.17 

7.06 

6.95 

6.85 

6.75 

6.65 

6.56 

6.47 


0.0682 
0.0705 
0.0728 
0.0751 
0.0773 
0.0795 
0.0818 
0.0841 
0.0863 
0.0886 
0.0908 
0.0931 
0.0953 
0.0976 
0.0998 
0.1020 
0.1043 
0.1065 
0.1087 
0.1109 
0.1131 
0.1153 
0.1175 
0.1197 
0.1219 
0.1241 
0.1263 
0.1285 
0.1307 
0.1329 
0.1350 
0.1372 
0.1394 
0.1416 
0.1438 
0.1460 
0.1482 
0.1503 
0.1525 
0.1547 


0.3623 
0.3652 
0.3680 
0.3707 
0.3733 
0.3759 
0.3784 
0.3808 
0.3832 
0.3855 
0.3877 
0.3899 
0.3920 
0.3941 
0.3962 
0.3982 
0.4002 
0.4021 
0.4040 
0.4059 
0.4077 
0.4095 
0.4113 
0.4130 
0.4147 
0.4164 
0.4180 
0.4196 
0.4212 
0.4227 
0.4242 
0.4257 
0.4272 
0.4287 
0.4302 
0.4316 
0.4330 
0.4344 
0.4358 
0.4371 


^ASIC  PRINCIPLES 


Properties  of 

Saturated  Steam — Continued 

^.2 

Total  Heat 
above  32°  F 

«l 

IS 

1^ 

.2 

£8 

S 

^ 

1 

is 

< 

1     -2 

ri 

1    •§ 
S    1 

4 

> 

fa- 

r 

o 

II 

|1 

53.3 

68 

301.0 

270.6 

1179.3 

908.7 

6.38 

0.1569 

0.4385 

1.1946 

54.3 

69 

302.0 

271.6 

1179.6 

908.0 

6.29 

0.1590 

0.4398 

1.1921 

55.3 

70 

302.9 

272.6 

1179.8 

907.2 

6.20 

0.1612 

0.4411 

1.1896 

56.3 

71 

303.9 

273.6 

1180.1 

906.5 

6.12 

0.1634 

0.4424 

1.1872 

57.3 

72 

304.8 

274.5 

1180.4 

905.8 

6.04 

0.1656 

0.4437 

1.1848 

58.3 

73 

305.8 

275.5 

1180.6 

905.1 

5.96 

0.1678 

0.4449 

1.1825 

59.3  . 

74 

306.7 

276.5 

1180.9 

904.4 

5.89 

0.1699 

0.4462 

1.1801 

60.3 

75 

307.6 

277.4 

1181.1 

903.7 

5.81 

0.1721 

0.4474 

1.1778 

61.3 

76 

308.5 

278.3 

1181.4 

903.0 

5.74 

0.1743 

0.4487 

1.1755 

62.3 

77 

309.4 

279.3 

1181.6 

902.3 

5.67 

0.1764 

0.4499 

1.1732 

63.3 

78 

310.3 

280.2 

1181.8 

901.7 

5.60 

0.1786 

0.4511 

1.1710 

64.3 

79 

311.2 

281.1 

1182.1 

901.0 

5.54 

0.1808 

0.4523 

1.1687 

65.3 

80 

312.0 

282.0 

1182.3 

900.3 

5.47 

0.1829 

0.4535 

1.1665 

66.3 

81 

312.9 

282.9 

1182.5 

899.7 

5.41 

0.1851 

0.4546 

1.1644 

67.3 

82 

313.8 

283.8 

1182.8 

899.0 

5.34 

0.1873 

0.4557 

1.1623 

68.3 

83 

314.6 

284.6 

1183.0 

898.4 

5.28 

0.1894 

0.4568 

1.1602 

69.3 

84 

315.4 

285.5 

1183.2 

897.7 

5.22 

0.1915 

0.4579 

1.1581 

70.3 

85 

316.3 

286.3 

1183.4 

897.1 

5.16 

0.1937 

0.4590 

1.1561 

71.3 

86 

317.1 

287.2 

1183.6 

896.4 

5.10 

0.1959 

0.4601 

1.1540 

72.3 

87 

317.9 

288.0 

1183.8 

895.8 

5.05 

0.1980 

0.4612 

1.1520 

73.3 

88 

318.7 

288.9 

1184.0 

895.2 

5.00 

0.2001 

0.4623 

1.1500 

74.3 

89 

319.5 

289.7 

1184.2 

894.6 

4.94 

0.2023 

0.4633 

1.1481 

75.3 

90 

320.3 

290.5 

1184.4 

893.9 

4.89 

0.2044 

0.4644 

1.1461 

76.3 

91 

321.1 

291.3 

1184.6 

893.3 

4.84 

0.2065 

0.4654 

1.1442 

77.3 

92 

321.8 

292.1 

1184.8 

892.7 

4.79 

0.2087 

0.4664 

1.1423 

78.3 

93 

322.6 

292.9 

1185.0 

892.1 

4.74 

0.2109 

0.4674 

1.1404 

79.3 

94 

323.4 

293.7 

1185.2 

891.5 

4.69 

0.2130 

0.4684 

1.1385 

80.3 

95 

324.1 

294.5 

1185.4 

890.9 

4.65 

0.2151 

0.4694 

1.1367 

81.3 

96 

324.9 

295.3 

1185.6 

890.3 

4.60 

0.2172 

0.4704 

1.1348 

82.3 

97 

325.6 

296.1 

1185.8 

889.7 

4.56 

0.2193 

0.4714 

1.1330 

83.3 

98 

326.4 

296.8 

1186.0 

889.2 

4.51 

0.2215 

0.4724 

1.1312 

84.3 

99 

327.1 

297.6 

1186.2 

888.6 

4.47 

0.2237 

0.4733 

1.1295 

85.3 

100 

327.8 

298.3 

1186.3 

888.0 

4.429 

0.2258 

0.4743 

1.1277 

87.3 

102 

329.3 

299.8 

1186.7 

886.9 

4.347 

0.2300 

0.4762 

1.1242 

89.3 

104 

330.7 

301.3 

1187.0 

885.8 

4.268 

0.2343 

0.4780 

1.1208 

91.3 

106 

332.0 

302.7 

1187.4 

884.7 

4.192 

0.2336 

0.4798 

1.1174 

93.3 

108 

333.4 

304.1 

1187.7 

883.6 

4.118 

0.2429 

0.4816 

1.1141 

95.3 

110 

334.8 

305.5 

1188.0 

882.5 

4.047 

0.2472 

0.4834 

1.1108 

97.3 

112 

336.1 

306.9 

1188.4 

881.4 

3.978 

0.2514 

0.4852 

1.1076 

99.3 

114 

337.4 

308.3 

1188.7 

880.4 

3.912 

0.2556 

0.4869 

1.1045 

BASIC  PRINCIPLES 


Properties  of  Saturated  Steam — Continued 


si 

if 
II 

1- 

Total  Heat 
above  32  °F 

^1 
1 

> 

0  . 

if 

2 

II 

5 

If 
11 

1     ^ 

1    ^ 

5  i 

•s 

1^ 

101.3 

116 

338.7 

309.6 

1189.0 

879.3 

3.848 

0.2599 

0.4886 

1.1014 

103.3 

118 

340.0 

311.0 

1189.3 

878.3 

3.786 

0.2641 

0.4903 

1.0984 

105.3 

120 

341.3 

312.3 

1189.6 

877.2 

3.726 

0.2683 

0.4919 

1.0954 

107.3 

122 

342.5 

313.6 

1189.8 

876.2 

3.668 

0.2726 

0.4935 

1.0924 

109.3 

124 

343.8 

314.9 

1190.1 

875.2 

3.611 

0.2769 

0.4951 

1.0895 

111.3 

126 

345.0 

316.2 

1190.4 

874.2 

3.556 

0.2812 

0.4967 

1.0865 

113.3 

128 

346.2 

317.4 

1190.7 

873.3 

3.504 

0.2854 

0.4982 

1.0837 

115.3 

130 

347.4 

318.6 

1191.0 

872.3 

3.452 

0.2897 

0.4998 

1.0809 

117.3 

132 

348.5 

319.9 

1191.2 

871.3 

3.402 

0.2939 

0.5013 

1.0782 

119.3 

134 

349.7 

321.1 

1191.3 

870.4 

3.354 

0.2981 

0.5028 

1.0755 

121.3 

136 

350.8 

322.3 

1191.7 

869.4 

3.308 

0.3023 

0.5043 

1.0728 

123.3 

138 

352.0 

323.4 

1192.6 

868.5 

3.263 

0.3065 

0.5057 

1.0702 

125:3 

140 

353.1 

324.6 

1192.2 

867.6 

3.219 

0.3107 

0.5072 

1.0675 

127.3 

142 

354.2 

325.8 

1192.5 

866.7 

3.175 

o.3r>o 

0.5086 

1.0649 

129.3 

144 

355.3 

326  9 

1192.7 

865.8 

3.133 

0.3192 

0.5100 

1.0624 

131.3 

146 

356.3 

328.0 

1192.9 

864.9 

3.092 

0.3234 

0.5114 

1.0599 

133.3 

148 

357.4 

329.1 

1193.2 

864.0 

3.052 

0.3276 

0.5128 

1.0574 

135.3 

150 

358.5 

330.2 

1193.4 

863.2 

3.012 

0.3320 

0.5142 

1.0550 

137.3 

152 

359.5 

331.4 

1193.6 

862.3 

2.974 

0.3362 

0.5155 

1.0525 

139.3 

154 

360.5 

332.4 

1193.8 

861.4 

2.938 

0.3404 

0.5169 

1.0501 

141.3 

156 

361.6 

333.5 

1194.1 

860.6 

2.902 

0.3446 

0.5182 

1.0477  • 

143.3 

158 

362.6 

334.6 

1194.3 

859.7 

2.868 

0.3488 

0.5195 

1.0454 

145.3 

160 

363.6 

335.6 

1194.5 

858.8 

2.834 

0.3529 

0.5208 

1.0431 

147.3 

162 

364.6 

336.7 

1194.7 

858.0 

2.801 

0.3570 

0.5220 

1.0409 

149.3 

164 

365.6 

337.7 

1194.9 

857.2 

2.769 

0.3612 

0.5233 

1.0387 

151.3 

166 

366.5 

338.7 

1195.1 

856.4 

2.737 

0.3654 

0.5245 

1.0365 

153.3 

168 

367.5 

339.7 

1195.3 

855.5 

2.706 

0.3696 

0.5257 

1.0343 

155.3 

170 

368.5 

340.7 

1195.4 

854.7 

2.675 

0.3738 

0.5269 

1.0321 

157.3 

172 

369.4 

341.7 

1195.6 

853.9 

2.645 

0.3780 

0.5281 

1.0300 

159.3 

174 

370.4 

342.7 

1195.8 

853.1 

2.616 

0.3822 

0.5293 

1.0278 

161.3 

176 

371.3 

343.7 

1196.0 

852.3 

2.588 

0.3864 

0.5305 

1.0257 

163.3 

178 

372.2 

344.7 

1196.2 

851.5 

2.560 

0.3906 

0.5317 

1.0235 

165.3 

180 

373.1 

345.6 

1196.4 

850.8 

2.533 

0.3948 

0.5328 

1.0215 

167.3 

182 

374.0 

346.6 

1196.6 

850.0 

2.507 

0.3989 

0.5339 

1.0195 

169.3 

184 

374.9 

347.6 

1196.8 

849.2 

2.481 

0.4031 

0.5351 

1.0174 

171.3 

186 

375.8 

348.5 

1196.9 

848.4 

2.455 

0.4073 

0.5362 

1:0154 

173.3 

188 

376.7 

349.4 

1197.1 

847.7 

2.430 

0.4115 

0.5373 

1.0134 

175.3 

190 

377.6 

350.4 

1197.3 

846.9 

2.406 

0.4157 

0.5384 

1.0114 

177.3 

192 

378.5 

351.3 

1197.4 

846.1 

2.381 

0.4199 

0.5395 

1.0095 

179.3 

194 

379.3 

352.2 

1197.6 

845.4 

2.358 

0.4241 

0.5405 

1.0076 

44 


BASIC  PRINCIPLES 


Properties  of   Saturated  Steam — 

Continued 

cT 

Total  Heat 

a 

^ 

fc- 

above  32°  F 

III 

f^ 

k 

< 

is 

r 

^1 

6 

r 

1 

cS 

1^ 

1     i 
>5    W 

In  the  Steam 

H 
Heat-Units. 

o 

u 

a  *-• 

181.3 

196 

380.2 

353.1 

1197.8 

844.7 

2.335 

0.4283 

0.5416 

1.0056 

183.3 

198 

381.0 

354.0 

1197.9 

843.9 

2.312 

0.4325 

0.5426 

1.0038 

185.3 

200 

381.9 

354.9 

1198.1 

843.2 

2.290 

0.437 

0.5437 

1.0019 

190.3 

205 

384.0 

357.1 

1198.5 

841.4 

2.237 

0.447 

0.5463 

0.9973 

195.3 

210 

386.0 

359.2 

1198.8 

839.6 

2.187 

0.457 

0.5488 

0.9928 

200.3 

215 

388.0 

361.4 

1199.2 

837.9 

2.138 

0.468 

0.5513 

0.9885 

205.3 

220 

389.9 

363.4 

1199.6 

836.2 

2.091 

0.478 

0.5538 

0.9841 

210.3 

225 

391.9 

365.5 

1199.9 

834.4 

2.046 

0.489 

0.5562 

0.9799 

215.3 

230 

393.8 

367.5 

1200.2 

832.8 

2.004 

0.499 

0.5586 

0.9758 

220.3 

235 

395.6 

369.4 

1200.6 

831.1 

1.964 

0.509 

0.5610 

0.9717 

225.3 

240 

397.4 

371.4 

1200.9 

829.5 

1.924 

0.520 

0.5633 

0.9676 

230.3 

245 

399.3 

373.3 

1201.2 

827.9 

1.887 

0.530 

0.5655 

0.9638 

235.3 

250 

401.1 

375.2 

1201.5 

826.3 

1.850 

0.541 

0.5676 

0.960O 

245.3 

260 

404.5 

378.9 

1202.1 

823.1 

1.782 

0.561 

0.5719 

0.9525 

255.3 

270 

407.9 

382.5 

1202.6 

820.1 

1.718 

0.582 

0.5760 

0.9454 

265.3 

280 

411.2 

386.0 

1203.1 

817.1 

1.658 

0.603 

0.5800 

0.9385 

275.3 

290 

414.4 

389.4 

1203.6 

814.2 

1.602 

0.624 

0.5840 

0.9316 

285.3 

300 

417.5 

392.7 

1204.1 

811.3 

1.551 

0.645 

0.5878 

0.9251 

295.3 

310 

420.5 

395.9 

1204.5 

808.5 

1.502 

0.666 

0.5915 

0.9187 

305.3 

320 

423.4 

399.1 

1204.9 

805.8 

1.4.56 

0.687 

9.5951 

0.9125 

315.3 

330 

426.3 

402.2 

1205.3 

803.1 

1.413 

0.708 

0.5986 

0.9065 

325.3 

340 

429.1 

405.3 

1205.7 

800.4 

1.372 

0.729 

0.6020 

0.9006 

335.3 

350 

431.9 

408.2 

1206.1 

797.8 

1.334 

0.750 

0.6053 

0.8949 

345.3 

360 

434.6 

411.2 

1206.4 

795.3 

1.298 

0.770 

0.6085 

0.8894 

355.3 

370 

437.2 

414.0 

1206.8 

792.8 

1.264 

0.791 

0.6116 

0.8840 

365.3 

380 

439.8 

416.8 

1207.1 

790.3 

1.231 

0.812 

0.6147 

0.8788 

375.3 

390 

442.3 

'419.5 

1207.4 

787.9 

1.200 

0.833 

0.6178 

0.8737 

385.3 

400 

444.8 

422 

1208 

786 

1.17 

0.86 

0.621 

0.868 

435.3 

450 

456.5 

435 

1209 

774 

1.04 

0.96 

0.635 

0.844 

485.3 

500 

467.3 

448 

1210 

762 

0.93 

1.08 

0.648 

0.822 

535.3 

550 

477.3 

459 

1210 

751 

0.83 

1.20 

0.659 

0.801 

585.3 

600 

486.6 

469 

1210 

741 

0.76 

1.32 

0.670 

0.783 

Source 

684 

500 

484 

1209 

725 

0.66 

1.52 

0.686 

0.755 

1062 

550 

542 

1200 

658 

0.42 

2.36 

0.743 

0.650 

1574 

600 

604 

1176 

572 

0.27 

3.75 

0.799 

0.540 

2265 

650 

441 

0.16 

6.2 

0.396 

2974 
3075 

689 
700 

0.05 

* 

* 

4.300.2 

752 

^FromG. 

A.  Goodenough's  ta 

bles  1915. 

t 

5017.1 

779 

|-Calculat( 

id  by  J.  McFarlane 

Gray—/ 

Voc.  In^i. 

M.E.,  July,  1889. 

t 

5659.9  ! 

810.6 

BASIC  PRINCIPLES 


45 


Properties  of  Superheated  Steam 

(Condensed  from  Marks  and  Davis'  Steam  Tables  and  Diagrams.) 

V  =  specific  volume  in  cu.  ft.  per  lb.,  h  =  total  heat,  from  water  at  32°  F.  in 

B.  t.  u.  per  lb.,  n  =  entropy,  from  water  at  32°. 


Press. 

Degrees  of  Superheat. 

Abs. 

Temp. 

Lbs. 

Sat. 

per 
Sq.  In. 

Steam. 

0 

50 

100 

loO 

200 

250 

300 

400 

500 

GOO 

20 

228.0 

V  20.08 

21.69 

23.25 

24.80 

26.33 

27.85 

29.37 

32.39 

35.40 

38.40 

h  1156.2 

1179.9 

1203.5 

1227.1 

1250.6 

1274.1 

1297.6 

1344.8 

1392.2 

1440.0 

n  1.7320 

1.7652 

1.7961 

1.8251 

1.8524 

1.8781 

1.9026 

1.9479 

1.9893 

2.0275 

40 

267.3 

V  10.49 

11.33 

12.13 

12.93 

13.70 

14.48 

15.25 

16.78 

18.30 

19.80 

h  1169.4 

1194.0 

1218.4 

1242.4 

1266.4 

1290.3 

1314.1 

1361.6 

1409.3 

1457.4 

n  1.6761 

1.7089 

1.7392 

1.7674 

1.7940 

1.8189 

1.8427 

1.8867 

1.9271 

1.9646 

60 

292.7 

v7.17 

7.75 

8.30 

8.84 

9.36 

9.89 

10.41 

11.43 

12.45 

13.46 

h  1177.0 

1202.6 

1227.6 

1252.1 

1276.4 

1300.4 

1324.3 

1372.2 

1420.0 

1468.2 

n  1.6432 

1.6761 

1.7062 

1.7342 

1.7603 

1.7849 

1.8081 

1.8511 

1.8908 

1.9279 

80 

312.0 

v5.47 

5.92 

6.34 

6.75 

7.17 

7.56 

7.95 

8.72 

9.49 

10.24 

h  1182.3 

1208.8 

1234.3 

1259.0 

1283.6 

1307.8 

1331.9 

1379.8 

1427.9 

1476.2 

n  1.6200 

1.6532 

1.6833 

1.7110 

1.7368 

1.7612 

1.7840 

1.8265 

1.8658 

1.9025 

100 

327.8 

V4.43 

4.79 

5.14 

5.47 

5.80 

6.12 

6.44 

7.07 

7.69 

8.31 

h  1186.3 

1213.8 

1239.7 

1264.7 

1289.4 

1313.6 

1337.8 

1385.9 

1434.1 

1482.5 

n  1.6020 

1.6358 

1.6658 

1.6933 

1.7188 

1.7428 

1.7656 

1.8079 

1.8468 

188.29 

120 

341.3 

V3.73 

4.04 

4.33 

4.62 

4.89 

5.17 

5.44 

5.96 

6.48 

6.99 

h  1189.6 

1217.9 

1244.1 

1269.3 

1294.1 

1318.4 

1342.7 

1391.0 

1439.4 

1487.8. 

n  1.5873 

1.6216 

1.6517 

1.6789 

1.7041 

1.7280 

1.7505 

1.7924 

1.8311 

1.8669 

140 

353.1 

V3.22 

3.49 

3.75 

4.00 

4.24 

4.48 

4.71 

5.16 

5.61 

6.06 

h  1192.2 

1221.4 

1248.0 

1273.3 

1298.2 

1322.6 

1346.9 

1395.4 

1443.8 

1492.4 

n  1.5747 

1.6096 

1.6395 

1.6666 

1.6916 

1.7152 

1.7376 

1.7792 

1.8177 

1.8533 

160 

363.6 

V2.83 

3.07 

3.30 

3.53 

3.74 

3.95 

4.15 

4.56 

4.95 

5.34 

h  1194.5 

1224.5 

1251.3 

1276.8 

1301.7 

1326.2 

1350.6 

1399.3 

1447.9 

1496.6 

n  1.5639 

1.5993 

1.6292 

1.6561 

1.6810 

1.7043 

1.7266 

1.7680 

1.8063 

1 .8418 

180 

373.1 

V2.53 

2.75 

2.96 

3.16 

3.35 

3.54 

3.72 

4.09 

4.44 

4.78 

h  1196.4 

1227.2 

1254.3 

1279.9 

1304. § 

1329.5 

1353.9 

1402.7 

1451.4 

1500.3 

n  1.5543 

1.5904 

1.6201 

1.6468 

1.6716 

1.6948 

1.7169 

1.7581 

1.7962 

1.8316 

200 

381.9 

V2.29 

2.49 

2.68 

2.86 

3.04 

3.21 

3.38 

3.71 

4.03 

4.34 

h  1198.1 

1229.8 

1257.1 

1282.6 

1307.7 

1332.4 

1357.0 

1405.9 

1454.7 

1503.7 

n  1.5456 

1.5823 

1.6120 

1.6385 

1.6632 

1.6862 

1.7082 

1.7493 

1.7872 

1.8225 

220 

389.9 

V2.09 

2.28 

2.45 

2.62 

2.78 

2.94 

3.10 

3.40 

3.69 

3.98 

h  1199.6 

1232.2 

1259.6 

1285.2 

1310.3 

1335.1 

1359.8 

1408.8 

1457.7 

1506.8 

n  1.5379 

1.5753 

1.6049 

1.6312 

1.6558 

1.6787 

1.7005 

1.7415 

1.7792 

1.8145 

240 

397.4 

vl.92 

2.09 

2.26 

2.42 

2.57 

2.71 

2.85 

3.13 

3.40 

3.67 

h  1200.9 

1234.3 

1261.9 

1287.6 

1312.8 

1337.6 

1362.3 

1411.5 

1460.5 

1509.8 

n  1.5309 

1.5690 

1.5985 

1.6246 

1.6492 

1.6720 

1.6937 

1.7344 

1.7721 

1.8072 

260 

404.5 

V  1.78 

1.94 

2.10 

2.24 

2.39 

2.52 

2.65 

2.91 

3.16 

3.41 

h  1202.1 

1236.4 

1264.1 

1289.9 

1315.1 

1340.0 

1364.7 

1414.0 

1463.2 

1512.5 

n  1.5244 

1.5631 

1.5926 

1.6186 

1.6430 

1.6658 

1.6874 

1.7280 

1.7655 

1.8005 

46 


BASIC  PRINCIPLES 


Properties  of  Superheated  Steam- 

—Continued 

Press. 
Abs. 

Temp. 

Sat. 
Steam. 

Degrees  of  Superheat. 

Lbs. 

per 

Sq.  In. 

0 

50 

100 

150 

200 

250 

300 

400 

500 

600 

280 

411.2 

V  1.66 

1.81 

1.95 

2.09 

2.22 

2.35 

2.48 

2.72 

2.95 

3.19 

h  1203.1 

1238.4 

1266.2 

1291.9 

1317.2 

1342.2 

1367.0 

1416.4 

1465.7 

1515.1 

n  1.5185 

1.5580 

1.5873 

1.6133 

1.6375 

1.6603 

1.6818 

1.7223 

1.7597 

1.7945 

300 

417.5 

V  1.55 

1.69 

1.83 

1.96 

2.09 

2.21 

2.33 

2.55 

2.77 

2.99 

h  1204.1 

1240.3 

1268.2 

1294.0 

1319.3 

1344.3 

1369.2 

1418.6 

1468.0 

1517.6 

n  1.5129 

1.5530 

1.5824 

1.6082 

1.6323 

1.6550 

1.6765 

1.7168 

1.7541 

1.7889 

350 

431.9 

V  1.33 

1.46 

1.58 

1.70 

1.81 

1.92 

2.02 

2.22 

2.41 

2.60 

h  1206.1 

1244.6 

1272.7 

1298.7 

1324.1 

1349.3 

1374.3 

1424.0 

1473.7 

1523.5 

n  1.5002 

1.5423 

1.5715 

1.5971 

1.6210 

1.6436 

1.6650 

1.7052 

1.7422 

1.7767 

400 

444.8 

V  1.17 

1.28 

1.40 

1.50 

1.60 

1.70 

1.79 

1.97 

2.14 

2.30 

h  1207.7 

1248.6 

1276.9 

1303.0 

1328.6 

1353.9 

1379.1 

1429.0 

147».9 

1528.9 

n  1.4894 

1.5336 

1.5625 

1.5880 

1.6117 

1.6342 

1.6554 

1.6955 

1.7323 

1.7666 

450 

456.5 

V  1.04 

1.14 

1.25 

1.35 

1.44 

1.53 

1.61 

1.77 

1.93 

2.07 

h  1209 

1252 

1281 

1307 

1333 

1358 

1383 

1434 

1484 

1534.0 

n  1.479 

1.526 

1.554 

1.580 

1.603 

1.626 

1.647 

1.687 

1.723 

1.758 

500 

467.3 

vO.93 

1.03 

1.13 

1.22 

1.31 

1.39 

1.47 

1.62 

1.76 

1.89 

h  1210 

1256 

1285 

1311 

1337 

1362 

1388 

1438 

1489 

1539 

n  1.470 

1.519 

1.548 

1.573 

1.597 

1.619 

1.640 

1.679 

1.715 

1.750 

Volume  of  Superheated  Steam — Linde's  equation  (1905), 
(150,300,000 


:^:;=0.5962T-/)(1 +0.0014/)) 


"ps 


-0.0833) 


in  which  p,  is  in  lb.  per  sq.  in.,  v,  is  in  cu.  ft.  and  T,  is  the  absolute  temperature  on  the  Fahren- 
heit scale,  has  been  used  in  the  computation  of  Marks  &  Davis'  steam  tables. 

Specific  heat  of  superheated  steam. — Mean  specific  heats  from  the  temperature  of  sat- 
uration to  various  temperatures  at  several  pressures — Knoblauch  and  Jakob  (from  Peabody's 
Tables) . 


Lb.  per  sq.  in. 

14.2 

28.4 

56.9 

85.3 

113.3 

142.2 

170.6 

199.1 

227.5 

256.0 

284.4 

Temp.  sat.  °F. 

210 

248 

289 

316 

336 

350 

368 

381 

392 

403 

412 

°F. 

°C. 

212 

100 

0.463 

302 

150 

.462 

0.478 

0.515 

392 

200 

.462 

.475 

.502 

0.530 

0.560 

0.597 

0.635 

0.677 

482 

250 

.463 

.474 

.495 

.514 

.532 

.552 

.570 

.588 

0.609 

0.635 

0.664 

572 

300 

.464 

.475 

.492 

.505 

.517 

.530 

.541 

.550 

.561 

.572 

.585 

662 

350 

.468 

.477 

.492 

.503 

.512 

.522 

.529 

.536 

.543 

.550 

.557 

752 

400 

.473 

.481 

.494 

.504 

.512 

.520 

.526 

.531 

.537 

.542 

.547 

THE  STEAM  ENGINE  47 


CHAPTER  2 

THE  STEAM  ENGINE 


Oues.     What  is  a  steam  engine? 

Ans.     A   machine  for  converting  heat  into  mechanical  power. 

Oues.  Into  what  three  classes  are  engines  divided  with 
respect  to  service? 

Ans.     Stationary,  marine  and  locomotive. 

Oues.  Into  what  two  classes  are  engines  divided  with 
respect  to  their  mode  of  operation? 

Ans.     Non-condensing  and  condensing. 

Oues.    What  is  a  non-condensing  engine? 

Ans.  A  non-condensing  engine  (sometimes  called  a  simple, 
or  high  pressure  engine)  is  one  that  exhausts  against  the  pressure 
of  the  atmosphere. 

Oues.     What  is  a  condensing  engine? 

Ans.  A  condensing  engine  is  one  that  exhausts  into  a  condenser 
or  device  which  condenses  the  exhaust  steam,  and  in  which,  by 
means  of  an  air  pump,  a  partial  vacuum  is  maintained,  thus 
reducing  the  back  pressure. 


48 


THE  STEAM  ENGINE 


THE  STEAM  ENGINE  49 

How  an  Engine  Works. — In  a  steam  engine,  heat  accom- 
plishes work  only  by  being  *'let  down"  from  a  higher  to  a  lower 
temperature ;  in  the  process  some  of  the  heat  is  converted  into 
useful  work.  The  mechanism  by  which  this  is  accomplished  is 
not  so  complicated  as  would  at  first  seem,  and  its  operation  is 
easily  understood. 

Fig.  54  is  a  sectional  plan  view  of  a  simple  form  of  steam  engine. 
C,  is  a  cylinder  into  which  steam  is  admitted  alternately  by  the 
valve  V,  through  the  steam  passages  S,  S'.  This  causes  a  steam 
tight  piston  P,  to  move  back  and  forth  in  the  C3dinder. 

The  pressure  of  the  steam  on  the  piston  is  transmitted  through 
a  piston  rod  to  a  connecting  rod  CR,  which  causes  the  crank  K, 
to  revolve;  thus,  the  reciprocating  motion  of  the  piston  is  trans- 
formed into  rotary  motion  of  the  crank.* 

In  the  revolution  of  the  crank,  the  connecting  rod  will  make  various 
angles  with  the  piston  rod,  hence,  to  allow  for  this,  a  cross  head  H,  is  placed 
at  the  point  where  the  two  rods  meet,  thus  forming  a  hinged  joint.  The 
cross  head  is  provided  with  guides  to  prevent  the  piston  rod  being  broken 
or  bent  by  the  oblique  thrusts  and  pulls  which  it  imparts  to  the  crank  by 
means  of  the  connecting  rod.  The  crank  is  keyed  or  forged  to  a  shaft  Z, 
upon  which  is  fastened  a  fly  wheel. 

In  the  operation  of  the  engine,  it  is  evident  that  while  steam  is  being 
admitted  at  one  end  of  the  cyhnder,  the  supply  already  in  the  cylinder 
from  the  previous  stroke,  must  be  exhausted  from  the  other  end.  This  is 
accomplished  by  means  of  a  slide  valve  V. 

The  two  steam  passages  S,  S',  connect  the  ends  of  the  cylinder  with  a 
box-like  projection  M,  called  the  steam  chest.  These  passages  terminate  in  a 
smooth  flat  surface  V  S,  known  as  the  valve  seat,  and  upon  which  the  valve 
moves ;  the  ends  of  the  passages  terminating  at  the  valve  seat  being  called 
the  ports.  Careful  distinction  should  be  made  between  the  terms  passages 
and  ports. 

The  two  ports  just  mentioned  are  called  the  steam  ports,  to  distinguish 
them  from  a  third  and  larger  port  located  midway  between  them  and 


*N0TE, — When  James  Watt  produced  his  "rotative  engine*"  in  1780  he  was  unable  to 
use  the  crank  because  it  had  already  been  patented  by  Matthew  Wasborough.  Watt  was 
not  discouraged  and  within  one  year  had  himself  patented  five  other  devices  for  obtaining 
rotary  motion  from  a  piston  rod. 


50 


STEAM  ENGINE  PARTS 


THE  STEAM  ENGINE  ,     51 


called  the  exhaust  port,  through  which  steam  passes  from  the  cylinder  to 
the  exhaust  pipe.  The  transverse  form  of  these  passages  is  long  and  narrow, 
so  that  steam  may  be  quickly  admitted  and  exhausted  from  the  engine 
with  only  a  slight  valve  movement. 

The  valve  itself,  is  a  rectangular  iron  box,  having  a  cavity,  similar  in 
form  to  the  letter  D.  The  size  of  the  valve  is  so  proportioned  that  in 
moving  back  and  forth  over  the  valve  seat  it  will  alternately  cover  and 
uncover  the  two  steam  ports,  allowing  steam  to  flow  alternately  into  the 
cylinder  ends  from  the  steam  chest. 

The  exhaust  cavity  EC.  connects  either  steam  port  to  the  exhaust  port, 
so  that  while  steam  is  being  admitted  to  one  end  of  the  cylinder  it  is  ex- 
hausted from  the  other  end. 

The  mechanism  which  imparts  the  to  and  fro  motion  to  the  valve  is 
called  the  valve  gear,  and  is  quite  similar  to  the  connections  between  the 
piston  and  crank. 

Instead  of  a  crank,  there  is  usually  an  eccentric  to  impart  motion  to  the 
valve.  This  consists  of  a  disc  bored  out  of  the  center  and  fastened  by  a 
key,  or  set  screw  to  the  shaft.  Around  the  eccentric  is  a  grooved  ring  called 
the  eccentric  strap.  Motion  is  transmitted  from  the  eccentric  to  the  valve  by 
means  of  an  eccentric  rod  and  valve  stem  as  shown,  a  valve  stem  guide 
being  provided  to  prevent  the  valve  stem  springing  out  of  position  on 
account  of  the  side  thrust  of  the  eccentric  rod.  By  turning  the  eccentric 
on  the  shaft,  the  relation  between  the  valve  movement  and  piston  move- 
ment may  be  changed,  hence,  the  eccentric  may  be  adjusted  so  as  to  give 
the  proper  distribution  of  steam  to  and  from  the  cylinder. 

In  the  figure,  the  piston  is  shown  at  the  end  of  the  cylinder  or  just  be- 
ginning the  stroke.  In  this  position,  the  piston  rod  and  eccentric  rod 
are  in  a  straight  line,  so  that  no  matter  how  much  steam  pressure  there 
may  be  on  the  piston  it  will  not  cause  the  crank  to  rotate.  This  happens 
when  the  piston  is  at  either  end  of  the  cylinder,  the  corresponding  positions 
of  the  crank  pin  being  called  dead  centers. 

To  prevent  the  engine  stopping  on  a  dead  center,  a  fly  wheel  having  a 
heavy  rim  is  provided,  which  by  its  momentum  keeps  the  engine  in  motion 
in  passing  these  centers. 

Owes.    Describe  the  operation  of  the  engine. 

Ans.  As  shown  in  fig.  54,  the  piston  is  at  the  beginning  of  the 
stroke  and  the  valve  has  just  begun  to  open  the  steam  port, 
admitting  steam  to  the  cylinder.  As  the  piston  moves,  the  valve 
opens  the  port  to  its  full  extent  and  closes  it  before  the  stroke  is 
completed,  thus  "cutting  off'*  the  supply  of  steam.  During 
these  ''events"  of  the  power  stroke  the  exhaust  cavity  of  the 


52  . 


THE  STEAM  ENGINE 


Figs.  55  to  61. — Diagrams  showing 
several  positions  of  the  piston,  valve, 
crank  and  eccentric  during  one 
stroke.  The  diagrams  show  the 
relative  movements  of  the  parts,  the 
crank  and  eccentric  positions  being 
shown  at  the  right. 


valve  connects  the  other  steam  port 
with  the  exhaust  port  E  allowing 
the  steam  which  was  admitted 
during  the  previous  stroke  to  ex- 
haust into  the  atmosphere,  or  con- 
denser, according  to  whether  the 
engine  be  run  non-condensing  or 
condensing. 


Since  the  supply  of  steam  is  cut  off 
by  the  valve  before  the  piston  completes 
the  stroke,  the  steam  in  the  cylinder 
expands  from  the  point  of  cut  off  until 
the  piston  has  almost  completed  the 
stroke.  It  is  released  at  this  point  by 
the  valve  connecting  the  proper  steam 
port  with  the  exhaust  port  E. 

The  movement  of  the  valve,  eccentric 
and  piston  during  one  revolution  of  the 
crank  may  be  more  easily  understood  by 
the  aid  of  a  series  of  diagrams,  figs.  55  to 
61.  The  crank  and  eccentric  positions 
corresponding  to  the  several  piston  and 
valve  positions,  are  shown  at  the  right. 

In  each  figure  the  center  of  the  crank 
pin,  center  of  the  shaft  and  the  eccen- 
tric are  shown  at  the  right. 

In  fig.  55  the  piston  is  at  the  beginning 
of  the  stroke;  the  valve  has  just  begun 
to  open  the  steam  port  to  the  left  for 
the  admission  of  steam,  w^hile  the  steam 
port  to  the  right  is  iuWy  open  for  ex- 
haust. To  bring  the  valve  in  this . 
position,  the  eccentric  has  been  set  in 
advance  of  the  crank  as  indicated.  The 
reason  for  this  will  be  explained  later. 

In  fig.  56,  the  piston  has  advanced  to 
the  right  about  Vio  of  the  stroke  and 
the  valve  has  moved  so  that  the  port 
at  the  left  is  nearly  wide  open  for  the 


THE  STEAM  ENGINE  53 


admission  of  steam.     Up  to  this  point  the  piston  and  valve  have  been 
moving  in  the  same  direction. 

The  valve  now  begins  its  return  stroke  and  when  the  piston  has  moved 
about  Vio  of  its  stroke,  the  valve  has  just  closed  the  port  at  the  left,  thus 
cutting  off  the  steam  supply  as  shown  in  fig.  57.'  The  steam  now  expands 
as  the  piston  continues  to  move,  but  during  this  interval  the  port  to  the 
right  is  gradually  being  closed  to  the  exhaust. 

When  the  piston  has  moved  about  Vio  of  its  stroke,  this  port  is  closed 
and  the  steam  remaining  in  the  cylinder  at  that  end  is  compressed  which 
helps  to  bring  the  piston  to  rest  without  jar  as  it  reaches  the  end  of  the 
stroke. 

The  velocity  of  the  piston  is  greatly  reduced  as  it  nears  the  end  of  the 
stroke  while  the  movement  of  the  valve  is  increased. 

In  fig.  59  when  the  piston  has  moved  only  slightly  from  its  position  in  the 
preceding  figure,  the  valve  is  at  the  point  of  opening  the  port  at  the  left 
to  release  the  stearii  for  exhaust. 

In  the  next  two  figures  the  piston  completes  its  stroke,  while  the  port 
at  the  left  is  being  very  rapidly  opened  to  exhaust. 

Fig.  61  shows  the  pistpn  at  the  end  of  the  stroke  and  the  valve  just  be- 
ginning to  admit  steam  to  the  port  at  the  right  for  the  return  stroke, 
completing  one  stroke,  the  same  cycle  of  events  being  repeated  for  the 
return  stroke. 

The  Expansion  of  Steam. — In  the  operation  of  a  steam 
engine,  steam,  as  just  explained,  is  admitted  and  exhausted 
alternately  at  the  ends  of  a  cylinder  within  which,  is  a  piston. 
The  force  exerted  by  the  steam  causes  the  piston  to  move  to  and 
fro  which  by  suitable  connections  is  made  to  do  useful  work. 
The  distance  the  piston  moves  in  either  direction  is  called  the 
stroke. 

*When  engines  are  required  to  exert  their  full  power  for  a  short  period 
as  happens,  for  instance,  when  a  locomotive  is  pulling  a  heavy  train  up  an 
incline,  steam  is  admitted  to  the  cylinder  at  full  pressure  through  the  greater 


*NOTE. — Steam  was  first  used  expansively  in  an  engine  by  Watt  who  in  making  appli- 
cation for  a  patent  said,  "My  improvement  in  steam  engines  consists  in  admitting  steam  into 
the  cyhnder,  or  steam  vessels  of  the  engine  only  during  some  part  or  portion  of  the  descent 
or  ascent  of  the  piston  of  said  cylinder,  and  using  the  elastic  forces,  wherewith  the  said  steam 
expands  itself  in  proceeding  to  occupy  larger  spaces  as  the  acting  powers  on  the  piston  through 
the  other  parts  or  portions  of  the  length  of  the  stroke  of  said  piston."  All  engines  now  operate 
^tt  this  principle  except  where  extraordinary  conditions  prevail. 


54 


THE  STEAM  ENGINE 


part  of  each  stroke,  without  regard  to  economy  in  its  use.  However,  this 
is  not  the  way  the  medium  is  ordinarily  used  in  an  engine,  for  although  an 
extra  amount  of  work  is  done,  it  is  at  the  expense  of  an  excessive  proportion 
of  steam  and  fuel  compared  with  the  gain  in  work. 


Boyle's  Law. — The  behavior  of  a  gas  in  expanding  has  been 
stated  by  Boyle  as  follows:  Tlie  pressure  of  a  perfect  gas  at 
constant  temperature  varies  inversely  as  its  volume."^ 


CENTER  CRANK 


>WIN&ING 
ECCElNTRiC 


SHAFT 
GOVERNOR 


Fig.  62. — The  Atlas  medium  speed  center  crank  engine  with  automatic  cut  off.  This  engine 
adjusts  its  power  output  to  meet  fluctuations  in  the  load  by  the  automatic  action  of  the 
shaft  governor  which  varies  the  point  of  cut  off.  Steam  is  expanded  to  a  higher  degree 
than  with  a  throttUng  engine  resulting  in  superior  economy. 


*N0TE. — The  student  should  distinguish  between  isothermal  and  adiabatic  expansion. 
Isothermal  expansion  means  expansion  at  constant  temperature;  adiabatic  expansion  denotes 
expansion  'Z£;t7^0M/  receiving  or  giving  up  heal.  It  should  be  noted  that  the  expansion  of  steam 
in  an  engine  cylinder  is  neither  isothermal  nor  adiabatic.  According  to  Rankin,  when  steam 
expands  in  a  closed  cylinder,  as  in  an  engine,  the  approximate  law  of  the  expansion  is 

P«<;  V~^°/9.  orPV*-"^=a  constant.  The  curve  constructed  from  this  formula  is  called  the 
adiabatic  curve.  The  author  does  not  believe  the  expansion  of  steam  even  approximately 
follows  the  adiabatic  curve,  and  may  be  said  to  depart  considerably  therefrom,  especially 
with  very  early  cut  off  where  the  effects  of  condensation  and  re-evaporation  are  marked.  Pea- 
body  says:  "It  is  probable  that  this  equation  (Rankin's  equation  above  mentioned)  was 
obtained  by  comparing  the  expansion  lines  on  a  large  number  of  indicator  diagrams."  He 
states  also  that  "there  does  not  appear  to  be  any  good  reason  for  using  an  exponential  equation 
in  this  connection."  Also  that  "the  action  of  a  lagged  steam  engine  cylinder  is  far  from  being 
adiabatic."  For  general  calculation  steam  may  be  taken  as  expanding  in  the  cylinder  according 
to  Boyle's  law,  above  given. 


THE  STEAM  ENGINE 


55 


This  law  may  be  illustrated  by  the  following  experiment:  In  fig.  63  is 
shown  a  cylinder,  having  a  piston  sliding  air  tight  in  its  length.  If  air  be 
compressed  in  front  of  the  piston  as  it  is  forced  from  one  end  toward  the 
other,  the  pressure  exerted  by  the  air  will  increase  in  ratio  as  the  volume 
is  diminished.  This  fact  may  be  shown  by  inserting  in  the  wall  of  the 
cylinder  at  different  points  a  number  of  tubes,  each  provided  with  an  air 
tight  piston  upon  which  bears  a  spiral  spring  holding  it,  as  at  A,  when  the 
pressure  on  the  piston  is  the  same  on  both  sides. 


Fig.  63. — Experiment  illustrating  Boyle's  law.  This  law  was  discovered  by  the  Hon.  Robert 
Boyle,  in  1660,  and  in  1661  he  presented  to  the  Royal  Society  his  work,  "Touching  the  Spring 
of  Air  and  its  Effects."  With  respect  to  the  experiment  on  air  he  says:  "  'Tis  evident 
that  as  common  air  when  reduced  to  half  its  natural  extent  obtained  a  spring  about  twice 
as  forcible  as  it  had  before,  so  the  air,  being  thus  compressed;  being  further  crowded  into 
half  this  narrow  space,  obtained  a  spring  as  strong  again  as  that  it  last  had,  and  conse- 
quently four  times  as  strong  as  that  of  common  air."  Boyle  does  not  appear  to  have  con- 
sidered his  law  to  possess  the  wide  application  afterwards  credited  to  it.  He  believed  that 
for  pressure  above  four  atmospheres,  the  compression  of  air  was  less  than  the  amount 
correspondmg  to  the  law. 

The  area  of  each  small  piston  is  assumed  to  be  one  square  inch,  and  the 
spring  of  such  a  tension  that  it  will  move  upward  through  one  of  the  spaces, 
between  the  horizontal  lines  on  the  diagram  with  each  ten  pounds  of  added 
•ressure.  in  the  large  cylinder. 


m 


56 


THE  STEAM  ENGINE 


Now  when  the  piston  moves  in  the  cylinder,  the  pressure  will  gradually  \ 
rise  due  to  the  compression  of  the  air  and  the  small  pistons  will  rise  against  I 
the  tension  of  the  springs  to  increasing  heights.  % 

As  the  piston  moves  from  the  end  of  the  cylinder  to  the  following  points:  \ 
initial  position,  3^  stroke  M  stroke  Y^  stroke  j 

the  positions  of  the  small  pistons  as  shown  in  the  figure  will  indicate  the  ; 
following  pressures: 

14.7  lbs.  29.4  lbs.  58.8  lbs.  117.6  lbs.  j 


Fig.  64. — To  describe  the  hyperbolic  curve  for  compression.  Draw  the  zero  or  vacuum  line  \ 
A  B,  (any  convenient  Scale)  =  length  of  stroke  or  volume  displaced  by  the  piston,  and  extend  - 
it  to  C,  making  A  C,  of  length  =  clearance,  that  is,  if  the  clearance  volume  be  say,  8  per  cent  "' 
of  piston  displacement  then  length  of  A  C  =8%  of  A  B,  or  .08  X A  B.  If  the  engine  be  running  ; 
non-condensing  and  exhausting  at  say  2  lbs.  gauge  pressure,  that  is  14.7+2=16.7  lbs.  ; 
absolute,  this  would  be  represented  by  a  horizontal  line  at  a  height  above  A  B,  corresponding  ; 
to  16.7  lbs.,  on  the  scale  of  pressures,  as  the  dotted  line  beginning  at  B'.  Suppose  the  exhaust  , 
valve  to  close  when  the  piston  has  reached  the  point  D,  corresponding  to  D'  in  the  diagram, 
then  C  D,  represents  the  volume  to  be  compressed.  By  Boyle's  law,  the  pressure  is  inversely  ■ 
proportional  to  the  volume,  hence,  when  the  piston  has  moved  to  E,  reducing  the  volume,  i 
one-half,  the  pressure  will  be  doubled  and  equal  to  16.7  X2  =33.4  lbs.  Measuring  up  from  E  i 
alength  corresponding  to  33.4  lbs.  gives  E',  a  point  on  the  curve.  Similarly,  when  the  ^ 
piston  moves  to  A,  compressing  to  one-quarter  the  original  volume  C  D,  the  pressure  rises  \ 
to  16.7  X4  =66.8  lbs.,  giving  the  point  A',  on  the  curve.  The  curve  may  be  described  through  i 
the  points  D',  E',  A',  just  obtained,  or  if  greater  accuracy  be  desired  more  points  may  be  \ 
obtained,  thus,  by  Boyle's  law,  pressure  Xvolume  =  constant,  from  which,  pressure  =  ' 
•  constant  -^volume.  If  C  D  =say,  3  ins.,  then  the  constant  =3  X16. 7  =50.1,  hence,  when  the  ^ 
piston  has  moved  to  any  point  as  F,  reducing  the  volume  to  2,  then  pressure  for  position  F,  =  '^ 
50.1  y2  =25.05  lbs.  abs.  Similarly,  other  points  may  be  obtained,  but  it  should  be  noted  : 
that  it  is  a  waste  of  time  to  obtain  more  than  say  4  points.  i 


THE  STEAM  ENGINE 


57 


thus  showing  that  if  the  volume  be  diminished  by  half,  the  pressure  is 
doubled.  If  a  curve  be  drawn  so  as  to  pass  through  the  center  of  each 
of  the  small  pistons,  it  will  show  the  pressure  corresponding  to  every  posi- 
tion of  the  large  piston. 

To  apply  this  to  the  conditions  of  operation  in  a  steam  engine,  it  may 
be  assumed  that  the  piston  has  moved  from  the  left  end  of  the  cylinder  to 
a  point  C,  or  3^  stroke,  and  during  this  time,  steam  is  admitted  at  a 
constant  pressure  of  58.8  lbs.  and  then  the  supply  cut  off. 

If  the  piston  now  move  to  B,  the  steam  w^ll  expand  to  double  its  volume 
and  its  pressure  will  be  reduced  to  half,  or  29.4  lbs. 


THROTTLE 
VALVE. 


SELF 
CONTAmEO 
OUTER  BEARING 


OVERHUNG  TYPE  CYLINDER 


SIDE  CRANK 


Fig.  65. — The  Houston,  Stanwood,  and  Gamble,  side  crank  self-contained,  throttling  engine. 
The  steam  supply  is  "throttled"  or  varied  automatically  by  the  governor  to  meet  load  changes, 
the  point  of  cut  off  being  the  same  for  all  loads.  This  type  of  engine  is  cheaper  than  an 
automatic  cut  off  engine  but  is  not  as  economical  in  the  use  of  steam. 

Again,  if  the  piston  move  to  the  end  of  the  stroke  (to  A)  the  volume  thus 
obtained  would  be  four  times  the  original  volume,  and  the  pressure  one- 
fourth  the  original  pressure,  or  14.7  lbs. 

The  curve  shows  the  expansion  of  the  steam  for  any  position  of  the 
piston  during  the  expansion  and  is,  therefore,  called  the  curve  of  expansion.* 


Oues.    What   curve    is  taken   ordinarily  to   represent 
tthe  expansion  of  steam  in  an  engine? 


58 


THE  STEAM  ENGINE 


Ans.     The  equilateral  or  rectangular  hyperbola  referred  to 

its  asymptotes.* 

The  Saving  due  to  Expansion. — The  advantage  of  using 

C  A'  D'  steam  expansively  may  be  clearly 

shown    by    a    diagram    as    in 

fig.    71,    which    represents    the 

work  done  by  an  engine  during 


C    A                1 

D 

M    E 

B 

S 

^ 

Fig.  66. — To  describe  the  hyberbolic  curve  for  expansion,  1st  method:  This  is  practically 
the  reverse  of  the  process  described  in  fig.  64.  As  before,  draw  the  zero  line  A  B  =  stroke  and 
volume  displaced  by  the  piston.  When  clearance  is  to  be  considered  extend  it  to  C,  making 
A  C  =clearance,  as  explained  in  fig.  64.  At  D,  piston  position  at  cut  off,  measure  vertically 
a  distance  =  pressure  at  cut  off  giving  the  point  D',  then  C  D',  represents  the  volume  of 
steam  admitted  considering  clearance,  and  A'  D',  the  volume  admitted  not  considering 
clearance.  Applying  Boyle's  law,  1,  considering  clearance,  when  the  initial  volume 
C  D,  is  doubled  by  expansion  to  point  E,  pressure  is  reduced  to  J^,  that  is  E  E'  =3^  D  D'. 
Similarly  G  G'  =3^  E  E',  or  34  D  D',  giving  the  points  D',E',G',  through  which  the  curve 
passes.  2^  If  clearance  be  not  con^/J^r^c?,  as  is  often  the  case,  the  initial  volume  is  taken  as 
A  D.^  Again  applying  Boyle's  law,  points  D'  M'  N'  are  obtained  giving  the  lower  curve. 
Considering  a  theoretical  diagram  the  error  introduced  by  not  considering  clearance  is  here 
indicated  by  the  shaded  area  D'  E'  B'  N'  M'  D',  however,  such  error  is  usually  allowed  for 
in  fixing  the  value  of  the  diagram  factor  as  explained  in  the  accompanying  text. 

^NOTE. — The  hyperbolic  curve  is  of  such  importance  that  it  should  be  thoroughly  under- 
stood. The  following  definitions,  accordingly,  should  be  carefully  noted:  Hyperbola. — A 
plane  curve  such  that  the  difference  of  the  distances  from  any  point  on  it  to  two  fixed  points,  called 
the  foci,  is  equal  to  a  given  distance.  The  line  passing  through  the  foci  and  terminating  at  the 
two  branches  of  the  curve  is  the  transverse  axis,  and  a  line  perpendicular  to  this  axis  drawn  half 
way  between  the  foci  is  the  conjugate  axis.  An  asymptote  of  a  hyperbola  is  a  right  line  which 
an  infinite  branch  of  the  curve  continually  approaches  but  does  not  reach,  in  other  words,  a  tangent 
to  the  curve  at  infinity.  The  equilateral  hyperbola. — A  hyperbola  whose  asymptotes  are  per- 
pendicular to  each  other.  This  is  the  form  of  hyperbola  which  represents  the  law  of  expansion 
of  steam,  or  Boyle's  law.  In  this  hyperbola,  the  product  of  the  abscissa  and  ordinate  at  any 
point  is  equal  to  the  product  of  abscissa  and  ordinate  of  any  other  point,  that  is,  if  p,  be  the 
ordinate  at  any  point  and  v,  its  abscissa  and  p'  and  v',  are  the  ordinate  and  abscissa  at  any 
other  point,  then  pv=p'v',  or  p  v=a.  constant.     See  Boyle's  law,  page  54.      Abscissae  and 


THE  STEAM  ENGINE 


59 


one  stroke.     As  in  the  preceding  figure  the  vertical  distances 
represent  pressures  and  horizontal  distances,  piston  positions. 

In  the  figure,  F  D,  is  the  length  of  the  stroke;  the  line  being  placed  at  such 
a  height  above  a  horizontal  hne  of  no  pressure,  that  any  point  on  it  is  at 
atmospheric  pressure.  This  line,  therefore,  is  called  the  atmospheric  lire 
in  distinction  from  the  line  of  no  pressure,  or  vacuum  line. 

The  distance  between  these  lines  depends  on  the  scale  used  in  measuring 
pressures,  thus,  if  Vio  inch  of  vertical  distance  be  taken  to  represent  one 
pound  pressure,  the  distance  between  the  lines  will  be  .1 X  14.7  =  1.47  inch. 

C'  A'    D'      I       2 

-         -r 


100 

90 

u 

-J 

< 
o 

80 
70 

60 

50 

\n 
if) 

UJ 

or 
a 

40 
30 
20 

ia.7 

10 


Fig.  67. — To  describe  the  hyperbolic  curve  for  expansion,  2nd  method:  Draw  the  zero 
line  A  B  =stroke,  and  extend  it  to  C,  making  A  C=clearance.  Take  the  distance  C  C — 
admission  pressure,  and  at  the  point  of  cut  off  D,  erect  the  perpendicular  D  D',  giving  the 
admission  line  A'  D'.  Extend  C  D'.  and  lay  off  any  number  of  points  1,  2,  3,  etc.  From  C, 
draw  radial  lines,  Cl,  C2,  C3,  etc.  Draw  horizontal  lines  through  1',  2',  3',  etc.,  and  vertical 
lines  through  1,  2,  3,  etc.    Their  intersections  1",  2",  3",  are  points  on  the  hyperbolic  curve. 

*NOTE.— Con^mwcJ. 
ordinates. — If  X  and  Y,  be  two  intersecting  axes,  X,  being  the  axis  of  abscissae,  and,  Y,  the 
axis  of  ordinates,  then,  the  distance  of  any  point  P,  from  the  Y  axis,  measured  parallel  to  the  axis 
of  X',  is  called  the  abscissa  of  the  point;  also,  the  distance  from  the  X  axis,  measured  parallel 
to  the  Y  axis  is  called  the  ordinate.  The  abscissa  and  ordinate  taken  together  are  called  the 
co-ordinates  of  the  point  P. 


60 


THE  STEAM  ENGINE 


CONJUGATE 
HYPERBOLA 


ASYMPTOTE 


TRANSVERSE 
AX15 


Y- ASYMPTOTE. 
OR  AXIS 
OF  PRESSURE 


'BRANCH  OF 

iHYPERBOLA  USED 
0  REPRESENT 
EXPANSION  AND 
COMPRtSSlONOF 
STEAM 


ASYMPTOTE 


Figs.  68  and  69. — ^Appearance  of  equilateral  hyperbola  1,  as  referred  to  its  rectangular  axes, 
fig.  68,  and  2,  as  referred  to  its  rectangular  asymptotes,  fig.  69,  one  branch  of  the  hyperbola 
in  this  position  being  used  to  represent  the  expansive  action  of  steam.  Comparing  the  two 
figures  it  will  be  noted  that  fig.  69  is  the  same  as  fig.  68,  rotated  through  45  degrees,  the  general 
method  of  constructing  the  hyperbole  in  fig.  69,  is  shown  in  fig.  70,  and  other  methods  in  the 
accompanying  diagrams. 


Fig.  70. — To  describe  an  equilateral  or  rectangular  hyperbola  referred  to  its  rectangular  v 
asymptotes.  General  method:  Draw  the  axis  of  volumes,  or  horizontal  asymptote  X  X',  | 
and  the  axis  of  pressures,  or  vertical  asymptote  Y  Y',  cutting  X  X',  at  O,  or  hyperbolic  center,  j 
Through  O,  draw  M  S,  at  45°  to  X  X'.  Take  any  point  on  M  S,  as  B,  and  with  radius  O  B,  j 
describe  a  circle,  cutting  M  S,  in  B  and  A,  giving  A  B,  the  transverse  axis.  At  B,  erect  a  t 
perpendicular  cutting  Y  Y',  at  D,  giving  O  D,  the  directrix.  With  O  D,  as  radius  describe  ;• 
a  circle  cutting  M  S,  at  F  and  F';  these  points  are  the  foci  of  the  hyperbola.  On  M  S,  take  i 
any  number  of  points  1,  2,  3,  etc.,  and  from  F,  and  F'  as  centers,  with  Al,  Bl,  A2,  B2,  etc.,  : 
as  radii,  describe  arcs  cutting  each  other  in  1',  2',  3',  etc.,  and  V\  2",  3",  etc.,  through  which  \ 
points  the  branch  H  B  G,  of  the  hyperbola  is  described.    Similarly,  the  other  branch  H  A  G,  j 


THE  STEAM  ENGINE 


61 


If  steam  be  admitted  at  say,  100  lbs.  per  square  inch  absolute  pressure 
when  the  piston  is  at  F,  and  the  supply  continued  at  constant  pressure 


f»CALE    or    VOLUME 

Fig.  71. — Theoretical  card  or  diagram  showing  the  theoretical   advantage  of   using   steam 
expansively. 


Fig,  70. — Continued. 

and  conjugate  hyperbola  shown  in  dotted  lines  may  be  described,  but  for  the  purpose  in  view, 
only  one  branch  H  B  6  need  be  described.  It  is  a  property  of  the  hyperbola  referred  to  its 
rectangular  asymptotes,  as  above,  that  if  one  asymptote  as  X  X',  be  taken  as  an  axis  of 
volumes  and  the  other  an  axis  of  pressures  measured  from  the  intersection  O,  then  for  any 
point  on  the  curve  as  B,  the  product  of  its  distance  from  Y  Y',  multiplied  by  its  distance  from 
X  X',  =  constant,  that  is  B  VXB  P=constant,  or  pressure  X volume  =  constant  which  is  in 
accordance  with  Boyle's  law. 


62 


THE  STEAM  ENGINE 


for  one-quarter  oi  the  stroke,  namely,  till  the  piston  reaches  E,  as  shown, 
this  may  be  represented  in  the  diagram  by  the  horizontal  line  AB,  drawn 
at  a  height  corresponding  to  100  lbs.  pressure. 

Now,  if  the  steam  be  released,  the  pressure  will  fall  to  that  of  the  atmos- 
phere as  indicated  by  the  line  BE,  and  the  work  done  for  each  square  inch 
of  piston  area,  will  be  equal  to  the  area  of  the  shaded  rectangle  ABEF,  or 
M,  because 

{load)  {distance  moved)  {area) 

work  done  =   AF     X  FE  =ABFE 

If,  instead  of  exhausting  the  steam  when  the  piston  has  made  only 
one-quarter  stroke,  the  supply  previously  admitted  be  retained  in  the 
cylinder  without  any  additional  supply,  and  be  allow^ed  to  expand,  the 


^THEORETICAL    DIAGRAM 

^ACTUAL  DIAGRAM 

■   LOSSES 


Fig.  72. — Comparison  of  theoretical  and  actual  diagrams  illustrated  by  solid  black  section  losses  ] 

in  the  actual  engine  which  reduce  the  theoretical  gain  due  to  expansion.  \ 

curve  of  expansion   BC  will  represent  the  gradual  fall  of  pressure  during  \ 

the  expansion.  { 

At  the  end  of  the  stroke,  the  absolute  pressure  C,  due  to  the  expansion  | 

is  called  the  terminal  pressure.    At  this  point,  the  steam  is  released  and  its  j 

pressure  falls  to  that  of  the  atmosphere  and  then  it  is  exhausted  as  in- .  I 

dicated  by  the  line  CD.  \ 

The  gain  due  to  expanding  the  steam  will  be  clearly  seen  by  noting  the 

size  of  the  four  sided  figure  BCDE,  or  S,  as  compared  with  the  shaded  ' 
figure  M.    This  area  S,  represents  the  work  done  by  the  steam  in  expanding 

just  as  the  shaded  area  M,  represents  the  work  of  the  steam  during  admission,  \ 

the  exact  amount  of  gain  being  determined  by  measuring  the  areas  of  M  j 

and  S,  and  dividing  the  combined  area  of  the  two  by  the  area  of  M,  that  is,  ' 

.M+S 


gain  by  expansion  =  - 


M 


The  method  of  measuring  these  areas  will  be  explained  later. 


THE  STEAM  ENGINE 


63 


r 

ii: 

\ 

§1 

.  c 

SI 

.  o 

/ 

bo 

^\^ 

/ 

..o 

^                 / 

.So 
be  . 

o                  / 

»-    '          / 

S5c 

3                  / 

■i|l 

O                / 

h.             / 

J-,  o-w 

^^^ 

0!  Y"^ 

egg 

»^  o  rt 

^.og 

-d^:^ 

■  m 

G       3 

C8  •-  o 

S  r- 

P 

/ 

G  O 

/ 

O  §  a; 

/ 

/ 

o.H  s 

w  O 
w  c  o 

^                          / 

o              / 

»-            / 

x  '  s 

o          / 

^  y 

^^^ 

i?.ii 

°^s 

^r.s 

O   rt   ^ 

-.  y  c2 

u- 

Ml 

■u.             / 

|§-i 

O           / 

^         / 

^^g 

3         / 

M_^-d 

O      / 

V 

w   0)  *- 

c'b  -S 

cc  rt  w 

m 

Q^-^ 

l^"-3 

O  o  o 

-tJ  "^  o 

^:S^ 

— 1 

:     ,:,..,  J      1      1      111     1 

To  illustrate  the  great  waste  which  re- 
sults in  admitting  steam  to  the  cylinder 
the  full  length  of  stroke,  as  in  the  case  of 
the  ordinary  steam  pump,  it  may  be 
assumed  that  instead  of  cutting  off  the 
supply  at  B,  it  be  continued  at  the  same 
pressure  to  the  end  of  the  stroke  as  rep- 
resented by  the  dotted  line  BG. 

If  now  the  steam  be  released,  its  pressure" 
will  fall  to  that  of  the  atmosphere  as  in- 
dicated by  the  line  GD,  and  the  work  done 
during  the  stroke  will  be  represented  by 
the  area  of  the  rectangle  AGDF. 

The  increase  in  power  secured  by  ad- 
mitting steam  for  full  stroke  instead  of 
cutting  off  at  one-quarter  stroke  and  ex- 
panding, is  indicated  by  the  area  of  the 
three  sided  figure  BGC.  To  obtain  this 
increase  in  power,  it  should  be  noted, 
requires  four  times  the  amount  of  steam 
as  when  cutting  off  at  one-quarter  stroke 
and  expanding. 

By  comparing  the  areas  of  the  figure,  it 
will  be  seen  that  in  admitting  steam  for 
full  stroke,  the  steam  consumption  is  ex- 
cessive, and  all  out  of  proportion  to  the 
gain  in  power. 


Cut  Oil. — When  steam  is  used 
expansively  in  a  cylinder,  it  is  ad- 
mitted during  a  portion  of  the  stroke 
at  a  constant  pressure,  and  then  the 
supply  suddenly  discontinued.  That 
point  of  the  stroke  in  which  this 
occurs  is  called  the  cut  off*  and  is 
usually  expressed  as  a  fraction  of  the 
stroke,  thus  J^,  H,  etc. 


s  s  §  ^  ^^2o   [3^  a 
3jLmosQV9gi        ^ 


*NOTE. — This  is  the   apparent    cut  off   as  dis- 
tinguished from  the  real  cut  off.  later  explained. 


64 


THE  STEAM  ENGINE 


Number  of  Expansions. — The  degree  in  which  steam  isi 
expanded  is  expressed  in  terms  of  the  original  volume,  thus,  fourj 
expansions  mean  that  steam  has  been  expanded  to  a  vohime| 
four  times  as  large  as  its  original  volume.  The  number  of! 
expansions  is  determined  by  the  cut  off.  ; 

Rule  1.      Number  of  expansions  equal  one  divided  by  the  cut  off,  * 


lUT   OFF 


Fig.  76. — Diagram  illustrating  initial  -pressure.  This  is  the  pressure  in  the  cylinder  at  the  he-  ] 
ginning  of  the  stroke  and  on  the  theoretical  diagram  is  assumed  to  remain  constant  up  to  the-  ' 
point  of  cut  off.  Some  initial  pressures:  Atmospheric  engines,  0  lbs.  gauge;  low  pressure  \ 
engines,  20  lbs.;  early  walking  beam  marine  engines,  25  lbs.;  later  types  50  to  75  lbs.;  j 
stationary  engines,  50  to  250  lbs.;  marine  screw  engines,  80  to  250;  locomotives,  150  to  275:  , 
locomobiles  and  special  engines,  250  to  500  lbs.  i 

Thus,  if  steam  be  cut  off  at  one-quarter  stroke,  .      \ 

4  I 

number  of  expansions  =  1  ^  J^  =  1  X-j--  =4.  I 

Rule  2. —  Number  of  expansions  equal  absolute  pressure  at  cut  \ 
off  divided  by  terminal  pressure. 

Thus  if  steam  be  expanded  from  100  lbs.  absolute  cut  off  pressure  to  20  1 
lbs.  absolute  terminal  pressure,  number  of  expansion  =  100 -^ 20  =  5.  j 


THE  STEAM  ENGINE 


65 


Initial  Pressure. — This  is  the  pressure  at  which  steam  is  ad- 
mitted to  the  cylinder,  and  should  not  be  confused  with  the  boiler 
pressure.*     It  is  theoretically  the  same  as  the  cut  off  pressure, 
but  in  practice  may  be  quite  different. 
C     A' D' 


TERMINAL  PRESSURE 


LOSS  DUE  TO 
PRE- RELEASE 


Fig.  77. — Diagram  illustrating  terminal  pressure.  The  valve  g'^ar  of  a  steam  engine  is  so 
constructed  that  exhaust  begins  before  the  piston  has  completed  the  stroke,  that  is,  the 
steam  is  pre-r pleased  when  the  piston  is  near  the  end  of  the  stroke,  so  that  (especially  in  the 
case  of  high  speed  engines)  the  pressure  of  the  steam  in  the  cylinder  will  be  reduced  as  near 
as  possible  to  the  exhaust  pressure  at  the  beginning  of  the  exhaust  stroke.  Theoretical 
calculations,  however,  are  simplified  by  assuming  that  exhaust  does  not  begin  till  the  end 
of  the  stroke.  Accordingly  the  pressure  at  that  point  due  to  expansion,  called  terminal  pressure, 
may  be  defined  as  the  imaginary  pressure  that  would  exist  in  the  cylinder  at  the  end  of  the 
stroke  if  the  steam  were  expanded  to  this  point  instead  of  being  pre-released.  Some  terminal 
pressures:  Single  cylinder  non-condensing  25  to  20  lbs.  abs.,  condensing  20  to  12;  multi- 
cylinder  condensing  12  to  5  lbs.  abs. 


*NOTE. — In  practice  the  initial  pressure  is  always  less  than  the  boiler  pressure  because 
of  the  resistance  offered  to  the  flow  of  steam  through  the  steam  pipe,  engine  ports  and  passages, 
especially  where  the  engine  is  at  some  distance  from  the  boiler  and  the  steam  line  contains 
numerous  elbows:  these  conditions  and  condensation  all  contribute  to  cause  drop  in  pressure 
between  boiler  and  engine.  In  ordinary  plants  this  drop  is  usually  two  or  more  pounds.  It 
should  be  noted  in  applying  Boyle's  law  that  absolute  pressures  should  be  used.  Thus,  90  \h. 
gauge  boiler  pressurie  with  2  lb.  drop  would  give  90+14.7  —  2  =  102.7  lbs.  absolute  initial 
pressure. 


66 


THE  STEAM  ENGINE 


Ones.     In   theoretical   calculations   what   assumption 
is  made  in  regard  to  the  initial  pressure? 

Ans.     It  is  assumed  to  remain  constant  during  admission, 
that  is  to  the  point  of  cut  off. 


-|OOX«O=I,00O  EXPANSION  CONSTANT 
1,000 -i- 15  =  bbV5  LB5. 
1,000-^20-50  LBS. 

1,009-  aS^^OLBS. 

1,000- 30  =  33 J^  LBS 


10  15  20 

VOLUME  SCALE 

Fig.  78. — Diagram  illustrating  the  expansion  constant  and  its  use.  According  to  Boyle's 
law,  pressure  Xvohcme  =  constant.  If,  as  indicated  in  the  diagram,  steam  be  admitted  to 
a  cylinder  during  10  inches  of  the  stroke  and  expanded  to  30  inches,  the  expansion  constant  = 
100  X 10  =  1,000,  from  which  the  pressure  at  any  other  point  =constant  -^volume,  that  is,  when 
the  piston  is  at 

15  ins.  20  ins.  25  ins.  30  ins. 

of  the  stroke,  the  expansion  constant  -^volume  is 

1,000^15  1,000-^20  1,000-^25  1,000-7-30 

which  is  equal  to 

m%  lbs.  50  lbs.  40  lbs.  33i^  lbs. 

Similarly  volume  =  constant -^pressure,  that  is,  when  the  pressure  due  to  the  expansion  is 

662^  lbs.  50  lbs.  40  lbs.  33^  lbs. 

the  expansion  constant -^pressure  is 

1,000^66^  1,000-^50  1,000^40  1,000 -^33K 

which  is  equal  to 

15  ins.  20  ins.  25  ins.  30  ins. 


Terminal  Pressure. — If  steam  he  expanded  to  the  end  of  the 
stroke,  the  pressure  at  that  point  is  called  the  terminal  pressure. 
It  is  determined  from  the  initial  pressure  and  the  number  of 
expansions. 


THE  STEAM  ENGINE 


67 


Rule.     The  terminal  pressure  equals  the  initial  pressure  divided 
by  the  number  of  expansions. 

Thus,  if  the  initial  pressure  be   100   lbs.  absolute,  and  the  number    of 
expansions  4, 

terminal  pressure  =  100 -^  4  =25  lbs.  absolute. 

Example. — If  the  initial  pressure  be  100  lbs.  gauge,  and  the  number  of 
expansions  be  4,  what  is  the  terminal  gauge  pressure? 
100  lbs.  gauge  =  100  +  14.7  =  114.7  lbs.  absolute. 
iiA  7^A  I  =28.69  lbs.  absolute,  or 
J14./  .4  (=.28.69-14.7=13.99  gauge. 


Fig.  79. — Diagram  illustrating  effect  of  expanding  to  a  terminal  pressure  less  than  the  exhaust 
pressure.  In  the  above  card,  representing  non-condensing  operation,  steam  is  expanded 
to  A,  below  the  exhaust  line,  giving  the  negative  area  S,  which  must  be  subtracted  from  M, 
to  obtain  the  effective  work  area. 


Expansion  Constant. — To  determine  the  pressure  at  any 
point  of  the  stroke,  use  is  made  of  a  constant  found  by  multi- 
plying the  volume  of  steam  at  cut  off  by  the  initial  pressure. 

For  instance,  if  steam  at  80  lbs.  absolute  pressure  be  cut  off  when  the 
piston  has  moved  10  inches  of  the  stroke,  then 

volume  X  pressure  =  constant 
substituting  the  above  values 
^  10     X      80      =      800 


68 


THE  STEAM  ENGINE 


Rule.     The  pressure  at  any  point  of  the  stroke  equals  the  ex- 
pansion constant  divided  by  the  volume  at  that  point. 

Thus,  when  the  piston  has  passed  through   20   inches   of   the   stroke 
the  pressure  at  that  point  is 

800 -^  20  =  40  lbs.  absohite. 

Rule.     The  volume  corresponding  to  any  pressure  is  equal  to 
the  expansion  constant  divided  by  the  pressure  at  that  point. 

Thus  when  the  pressure  has  decreased  to  40  lbs.  absolute,  the  volume 
corresponding  as  measured  by  the  piston  movement  is 

800-1-40  =  20  inches 

A  A 


Figs.  80  and  81. — Theoretical  cards  illustrating  mean  forward  pressure  and  back  pressure. 

The  two  cards  are  the  same  as  the  card  in  fig.  78.  If  in  fig.  78  an  ordinate  be  drawn  through 
the  middle  of  each  of  the  areas  CDC  D',  D'  H  F  D,  etc.,  they  will  appear  in  fig.  80  as  the 
dotted  vertical  lines  A  B,  C  D,  E  F,  etc.  The  mean  forward  pressure  represented  by  the 
area  of  M  -i-its  length  L  L'  X  the  pressure  scale,  is  equal  to  the  average  of  the  ordinates, 
that   is,   their  sum   divided   by   the   number,   and   multiplied   by   the  pressure  scale,  or 

(AB-hCD+EF+GH+IJ)^  ,        o-    -i    i     •     ^      oi     *i.     ,.     , 

•^^ ^ — —  Xpressure  scale.     Similarly  in  fig.  81,   the  back  pressure. 


=  area  S  -v-  its  length  L  L'  X  pressure  scale 


A'  B  +  C  D  +  E'  F+G'  H+V  J 


X  pressure 


scale,  or  since  in  this  case  all  are  of  the  same  length,  back  pressure  = 
sure  scale. 


height  of  S  X  pres- 


Mean  Effective  Pressure. — In  the  diagrams,  figs.  82  and 
83,  the  effective  pressure  which  tends  to  move  the  piston  is 
clearly  the  difference  between  the  steam  pressure  acting  on  one 
face  of  the  piston  and  the  atmospheric  pressure  acting  on  the 
other  face  in  the  opposite  direction. 

The  steam  pressure  acting  in  the  direction  in  which  the  piston  moves  is 
called  the  forward  pressure,  and  any  pressure  as  that  of  the  atmosphere 


THE  STEAM  ENGINE 


69 


acting  on  the  opposite  face,  and  opposing  the  movement  of  the  piston  is 
called  the  hack  pressure. 

If  steam  be  expanded  as  in  the  diagram,  its  pressure  will  vary,  hence  it 
is  necessary  to  find  an  average  or  mean  pressure  which  shall  be  the  equivalent 
vine:  forward  pressure. 


of  this  varying  forward  pressure. 


The  mean  elective  pressure  is  equal  to  the  difference  between 
the  mean  forward  pressure  and  the  mean  hack  pressure.  That  is, 
the  mean  effective  pressure,  or 

M.E.  P.  =  mean  forward  pressure — mean  hack  pressure. "^ 


Figs.  82  and  83. — Theoretical  cards  illustrating  mean  effective  pressure:  fig.  82,  constant 
back  pressure;  fig.  83,  variable  back  pressure.  Since  the  back  pressure  directly  opposes 
the  forward  pressure,  evidently  the  net  or  actual  pressure  tending  to  move  a  piston,  or 
mean  effective  pressure  is  the  difference  between  these  two  pressures,  that  is,  Af .  E.  P.  =mean 
forward  pressure  —  back  pressure.  In  fig.  80  the  mean  forward  pressure  is  figured  from  the 
area  M,  and  in  fig.  81,  the  back  pressure  from  the  area  S,  hence,  the  mean  effective  pressure 
must  depend  on  the  difference  of  these  two  areas,  that  is  M  —  S,  or  M'  as  shown  in  fig.  82, 
when  the  back  pressure  is  constant.  Where  compression  is  taken  into  account,  as  in  fig,  83, 
evidently  M.  E.  P.  =mean  forward  Pressure —  mean  back  pressure,  but  in  the  figure,  the 
mean  back  pressure  is  figured  from  area  S+area  S',  hence,  in  this  case  M.  E.  P.  depends  on 
the  difference  between  area  M  in  fig.  80  and  areas  S+S'  in  fig.  83,  and  giving  the  area  M" 
where  average  ordinate  XPressure  scale=M.  E.  P, 


If  the  distance  of  all  points  on  the  expansion  line  from  the  vacuum  line 
be  measured,  and  the  sum  of  these  distances  be  divided  by  their  number, 
the  quotient  will  equal  the  mean  forward  pressure;  from  which  is  deducted 
the  back  pressure,  both  in  pounds  absolute,  and  the  result  will  be  the  mean 
effective  pressure. 


*NOTE. — In  the  theoretical  card,  fig.  82,  the  back  pressure  S,  is  constant,  but  in  practice 
it  varies,  hence  in  the  actual  card,  the  mean  effective  pressure  =mean  forward  pressure — mean 
back  pressure.  It  should  be  noted  that  in  a  theoretical  card,  taking  into  account  compression, 
the  mean  back  pressure  must  be  subtracted  from  the  mean  forward  pressure  to  obtain  the 
M.  E.  P. 


70 


THE  STEAM  ENGINE 


Hyperboiic  Logarithms. — In  the  diagram,  fig.  84,  the  exact 
value  of  the  area  S,  may  be  readily  obtained  by  referring  to  a 
table  of  hyperbolic  logarithms;  for,  since  the  cvirve  of  expansion 
is  an  hyperbola,  the  hyperbolic  logarithm  of  the  number  of 
expansions  expresses  the  relation  between  the  area  S,  during 
expansion  and  the  area  M  during  admission.  That  is,  if 
admission  area  M  =  unity 
A_ B 


M+S  «l+ HYPERBOLIC    LOGARITHM 


Fig.  84.— Reproduction  in  part  of  fig.  71,  showing  the  application  of  the  hyperboHc  logarithm 
in  finding  the  mean  effective  pressure. 


and 


expansion    area    S  =  hyperbolic  logarithm 
total  area  M.-\-S  =  l-\-  hyperbolic  logarithm 


Thus,  if  steam  be  cut  off  at  one-quarter  stroke,  it  is  expanded  to  4  times 
its  original  volume;  then  if  the  area  during  admission  =  1,  the  area  during 
expansion  =  the  hyperbolic  logarithm  of  4. 

Now,  turning  to  the  table  of  hyperbolic  logarithms  on  page  71,  the 
hyp.  log.  of  4  is  1.3863.  This  is  the  theoretical  gain  by  expansion,  that  is, 
if  1  represent  the  work  M,  done  before  expansion,  the  work  S,  done  during 
expansion  is  1.3863  times  greater  than  the  work  M,  done  before  expansion. 


THE  STEAM  ENGINE 


71 


The  total  work  done  during  the  stroke  is  equal  to 

M+S  =  l+%^  log.  4  =  1+1.3863=2.3863 
Hence,  over  twice  the  work  is  done  by  admitting  steam  one-quarter 


Table  of  Hyperbolic  Logarithms 

No. 

Hyp.  log. 

No. 

Hyp.  log. 

No. 

Hyp.  log. 

No. 

Hyp.  log. 

1.1 

0.0953 

4.5 

1.5041 

7.9 

2.0669 

19.0 

2.9444 

1.2 

0.1823 

4.6 

1.5261 

8.0 

2.0794 

20.0 

2.9957   • 

1.3 

0.2624 

4.7 

1.5476 

8.1 

2.0919 

21.0 

3.0445 

1.4 

0.3365 

4.8 

1.5686 

8.2 

2.1041 

22.0 

3.0910 

1.5 

0.4055 

4.9 

1.5892 

8.3 

2.1163 

23.0 

3.1355 

1.6 

0.4700 

5.0 

1.6094 

8.4 

2.1282 

24.0 

3.1781 

1.7 

0.5306 

5.1 

1.6292 

8.5 

2.1401 

25.0 

3.2189 

1.8 

0.5878 

5.2 

1.6487 

8.6 

2.1518 

26.0 

3.2581 

1.9 

0.6419 

5.3 

1.6677 

8.7 

2.1633 

27.0 

3.2958 

2.0 

0.6931 

5.4 

1.6864 

8.8 

2.1748 

28.0 

3.3322 

2.1 

0.7419 

5.5 

1.7047 

8.9 

2.1861 

29.0 

3.3673 

2.2 

0.7885 

5.6 

1.7228 

9.0 

2.1972 

30.0 

3.4012 

2.3 

0.8329 

5.7 

1.7405 

9.1 

2.2083 

31.0 

3.4340 

2.4 

0.8755 

5.8 

1.7579 

9.2 

2.2192 

32.0 

3.4657 

2.5 

0.9163 

5.9 

1.7750 

9.3 

2.2300 

33.0 

3.4965 

2.6 

0.9555 

6.0 

1.7918 

9.4 

2.2407 

34.0 

3.5263 

2.7 

0.9933 

6.1 

.1.8083 

9.5 

2.2513 

35.0 

3.5553 

2.8 

1.0296 

6.2 

1.8245 

9.6 

2.2618 

36.0 

3.5835 

2.9 

1.0647 

6.3 

1.8405 

9.7 

2.2721 

37.0 

3.6109 

3.0 

1.0986 

6.4 

1.8563 

9.8 

2.2824 

38.0 

3.6376 

3.1 

1.1312 

6.5 

1.8718 

9.9 

2.2925 

39.0 

3.6636 

3.2 

1.1632 

6.6 

1.8871 

10.0 

2.3026 

40.0 

3.6889 

3.3 

1.1939 

6.7 

1.9021 

10.5 

2.3513 

41.0 

3.7136 

3.4 

1.2238 

6.8 

1.9169 

11.0 

2.3979 

42.0 

3.7377  ' 

3.5 

1.2528 

6.9 

1.9315 

11.5 

2.4430 

43.0 

3.7612 

3.6 

1.2809 

7.0 

1.9459 

12.0 

2.4849 

44.0 

3.7842 

3.7 

1.3083 

7.1 

1.9601 

12.5 

2.5262 

45.0 

3.8067 

3.8 

1.3350 

7.2 

1.9741 

13.0 

2.5649 

46.0 

3.8286 

3.9 

1.3610 

7.3 

1.9879 

13.5 

2.6027 

47.0 

3.8501    : 

4.0 

1.3863 

7.4 

2.0015 

14.0 

2.6391 

48.0 

3.8712  , 

4.1 

1.4110 

7.5 

2.0149 

15.0 

2.7081 

49.0 

3.8918 

4.2 

1.4351 

7.6 

2.0281 

16.0 

2.7726 

50.0 

3.9120 

4.3 

1.4586 

7.7 

2.0412 

17.0 

2.8332 

4.4 

1.4816 

7.8 

2.0541 

18.0 

2.8904 

' 

NOTE. — Hyperbolic   or    Naperian  logarithms   are   common   logarithms    multiplied    by 
2.3025851. 


72  THE  STEAM  ENGINE 


stroke  and  expanding  four  times  than  by  admitting  steam  one-quarter 
stroke  and  exhausting  at  that  point  into  the  atmosphere. 

If  the  distance  F  E  be  called  1,  then  4  expansions  F  D  =4.  Now,  if  the 
total  area  M+S,  be  divided  by  F  D,  or  4,  it  will  give  the  height  of  a  rectangle 
whose  area  =  M-|-S,  and  the  height  of  this  rectangle  will  represent  the  mean 
effective  pressure,  hence: 

Rule. — To  find  the  mean  effective  pressure,  multiply  the  initial 
pressure  in  lbs.  absolute  hy  1+hyp.  log.  of  the  number  of  ex- 
pansions, and  divide  by  the  number  of  expansions.  From  the 
quotient,  subtract  the  absolute  back  pressure. 

In  the  form  of  an  equation  the  mean  effective  pressure  or 

-  -.  ^  ^      initial  pressure  abs  .XI  -\-  hyp .  log  .no.  of  expansions     ,     , 

M.E.P.= ^ 1 j-^ — ^: -^ — ^ back  pressure  abs, 

number  of  expansions 

or,  expressed  in  the  usual  symbols 


It  should  be  remembered  that  the  initial  pressure  P,    and 
back  pressure  B.  P.,  are  taken  in  lbs.  absolute. 

Example, — What  is  the  mean  effective  pressure,  with  80  lbs.  initial 
gauge  pressure,  one- third  cut  off,  16  lbs.  absolute  back  pressure? 

Initial  pressure  absolute  =  80 + 14.7  =  94.7  lbs. 

Number  of  expansions  =  1  -i- Va  =  1  X^A  =3. 

Hyp.  log.  of  3  (from  table  page  71)  =1.0986. 

1+hyp.  log  3  =  1+1.0986=2.0986. 

TVT          «    ^'                       94.7X2.0986       _     .^  o  iu 
Mean  effective  pressure  = 16  =  o0.2  lbs. 


Oues.  In  the  operation  of  an  engine  is  there  as  much 
advantage  from  working  steam  expansively  as  the  above 
calculations   indicate? 


THE  STEAM  ENGINE 


73 


Ans.  No;  it  is  not  possible  in  steam  engines  to  convert  all  the 
energy  of  the  steam  into  useful  work.  There  are  various  losses 
due  to  leakage,  radiation,  condensation  and  other  causes,  all  of 
which  tend  to  make  the  actual  mean  effective  pressure  obtained  in 
an  engine  less  than  that  calculated,  as  shown  in  fig.  85, 


Table  for  Finding  Mean  Pressure 


Number 

of 

expansions 

1  +hyp.  log.  r 
r 

Number 

of 
expansions 

1  +hyp.  log.  r 

r 

1.0 
1.5 
2.0 
2.5 
3.0 
3.5 
4.0 
4.5 
5.0 
5.5 
6.0 
7.0 
8.0 
9.0 
10.0 

1.00 

0.937 

0.847 

0.766 

0.700 

0.644     • 

0.597 

0.556 

0.522 

0.492 

0.465 

0.421 

0.385 

0.355 

0.330 

11.0 
12.0 
13.0 
14.0 
15.0 
16.0 
17.0 
18.0 
19.0 
20.0 
21.0 
22.0 
23.0 
24.0 
25.0 

0.309 
0.290 
0.274 
0.260 
0.247 
0.236 
0.226 
0.216 
0.208 
0.200 
0.192 
0.186 
0.180 
0.174 
0.169 

How  to  Use  the  Table. — The  mean  pressure  is  obtained  for 
any  number  of  expansions  by  multiplying  the  initial  pressure 
absolute  by  the  factor  given. 

Example. — What  is  the  mean  pressure  of  steam  for  100  lbs.  initial  gauge 
pressure,  and  one-quarter  cut  off? 

100    lbs.    gauge    pressure  =  100+14.7  =  114.7    lbs.    absolute    pressure; 
J^cut-off  =  1  -7-  3^  =  4  expansions.  ♦ 

In  the  table  the  factor  for  four  expansions  is  .597,  from  which  the  mean 
pressure  is 

1 14.7 X. 597  =  68.5  lbs. 

To  find  the  mean  effective  pressure,  the  absolute  back  pressure  is  subtracted 
from  the  mean  forward  pressure  just  obtained. 


74 


THE  STEAM  ENGINE 


Thus  in  the  example  just  given,  if  the  engine  be  running  non-condensing, 
and  exhausting  against  a  back  pressure  of  2  lbs.  gauge,  then  the  absolute 
back  pressure  =  24-14.7  =  16.7  and  the  mean  effective  pressure  =  68.5  — 16.7 
=  51.8  lbs. 

Again,  if  the  engine  be  running  condensing  with  a  28  inch  vacuum,  the 
absolute  pressure  corresponding  to  this  vacuum  is,  from  the  steam  table 
on  page  40,  .946  lbs.  absolute,  and  the  mean  effective  pressure  is 
68.5  — .946  =67.55  lbs. 


Diagram  Factor. — From  the  answer  to  the  last  question, 
(page  73),  it  is  seen  that  no  such  results  are  obtained  in  the 

PRE-ADM15SI0N  LOSS 

-LOSS  BETWEEN  BOILER  AND    ENGINE 
ADMISSION  LOSS 

LOSS  DUE  TO  DROP  AT   CUT  OFF 
-AND    CONDENSATION 

RE-EVAPORATION   GAIN 

PRE-RELEASE 
LOSS 


INITIAL 

EXHAUST 

LOSS 


,  COMPRESSION 
LOSS 


EXHAUST  LOSS 


ATMOSPHERIC    LINE 
ZERO     LINE 


Fig.  85. — Comparison  of  theoretical  and  actual  cards  showing  the  various  losses  which  tend 
to  reduce  the  area  of  the  actual  card,  making  it  in  some  cases  considerably  less  than  that  of 
the  theoretical  card.  In  the  figure,  A  B  C  D  E  A,  is  the  theoretical  card  and  A'  B'  C  D'  E'  F  A', 
the  actual  card.  In  practice,  an  initial  loss  occurs  in  getting  the  steam  from  the  boiler  to  the 
engine  making  the  beginning  of  the  actual  card  at  A'  instead  of  A.  During  admission,  the 
pressure  drops  because  of  friction  through  ports  and  passages,  becoming  very  pronounced 
at  cut  oflF  by  "wire  drawing."  During  expansion,  the  curve  at  first  is  below  the  theoretical 
because  of  loss  of  pressure  at  cut  off,  later  condensation,  and  re-evaporation  causes  it  to 
rise  slightly  above  before  pre-release.  During  pre-release  the  pressure  drops  very  quickly, 
but  does  not  reach  exhaust  pressure  until  the  piston  has  begun  the  exhaust  stroke.  During 
exhaust,  the  pressure  is  always  greater  in  the  cylinder  than  the  external  back  pressure  of 
the  atmosphere  or  condenser.  During  compression,  sometimes  considerable  area  of  card  is 
lost.  During  pre-admission  the  steam  is  retarded  in  rising  to  admission  pressure  because 
of  wire  drawing,  this  loss  during  this  period  is  very  small,  and  in  some  cases  not  noticeable 
especially  if  there  h%  liberal  lead  because  the  piston  is  practically  stationary. 

actual  engine,  as  in  theoretical  calculations.  The  diagram,  fig.  84 
is  known  as  a  theoretical  (indicator)  card  and  represents  a  perfect 
performance,  assuming  hyperbolic  expansion,  that  is,  if  the  valves 


THE  STEAM  ENGINE 


75 


U- 

oo 

Q 

1 

U-.   . 

w 

OUJ 

--> 

/w^ 

> 

II,  Jn^ 

i-q: 

\  jW 

=33 

nriJL 

'w^ 

^o 

<*.^ 

<^ 

-J 

< 

ID 

f 

H^ 

^y^ 

^V    A 

«$y 

y 

V 

GO 

^ 

LJ 
O 

-J 

i 

U 

< 

y 

^^^ 

w^. 

LU 

/ 

§•'2  ^.S  a;<  >,'^  S-S  II 


<.5 


1:0  o 


;    ^^JH.^   rt   ^   g   ^j 


g    tnW    0^    "    Vh    (U  .4)7 

S  S<:  g  j:^^  y^  g-^  -I- 


^^«a)bc<u'ort;r5    rll 

^S:e-o3'S'5-ii  s 

.0-2  .§0.0^ 


C  <U  (U   o   » 


op§rt"gi;<<a55^g 


00 


could  open  and  close 
instantly,  avoiding 
**wire  drawing"  or 
loss  of  pressure  while 
not  fully  open  or 
closed. 

If  there  were  no  con- 
densation, or  any  other 
condition  causing  a  loss 
of  pressure,  the  diagram, 
fig.  84,  would  represent 
the  performance  of  an 
engine  working  under 
such  conditions. 

In  practice,  as  be- 
fore stated  no  suck 
results  are  possible,  a 
diagram  of  less  area 
(which  means  less 
work)  being  obtain- 
ed. This  diagram  is 
obtained  by  means  of 
an  indicator  and  is 
called  the  actual  or 
indicator  diagram  to 
distinguish  it  from 
the  theoretical  dia- 
gram which  is  con- 
structed from  the 
calculated  perform- 
ance. The  relative 
value  of  these  dia- 
grams is  expressed 
bv    a    coefficient 


76 


THE  STEAM  ENGINE 


called  the  diagram  factor,  which  may  be  defined  as  the  ratio 
of  the  actual  card  area  to  the  theoretical  card  area,  that  is 
,.  i.      .  ci'^^CL  of  actual  card 

diagram  factor  = --^- 7—, r 

area   of  theoretical   card 

Remembering  that  the  work  represented  by  the  actual  card,  that  is, 
its  area,  is  always  less  than  the  area  of  the  theoretical  card,  it  must  be 
evident  that  if  an  engine  cylinder  be  proportioned  for  a  certain  horse  power, 
based  on  mean  effective  pressure  of  the  theoretical  card,  it  will,  when  built 
and  tested,  develop  less  power  because  of  the  various  conditions  before 
mentioned  which  tend  to  reduce  this  pressure,  or  theoretical  mean  effective 


Fig.  88. — Theoretical  and  "expected"  cards  of  Corliss  engine  operating  under  conditions  given 
in  example  on  page  97.  After  drawing  the  theoretical  card  A  B  C  D  E,  to  correspond  with 
the  given  operating  condition,  the  designer  inscribes  or  sketches  within  the  expected  card 
making  such  allowance  for  the  various  losses  as  his  experience  and  judgment  dictates. 
The  M.  E.  P.  can  be  obtained,  1,  by  finding  the  diagram  factor  and  multiplying  it  by  the 
theoretical  M.  E.  P.,  or  2,  by  finding  the  expected  M.  E.  P.  direct  from  the  expected  card. 
Clearly,  the  first  method  would  be  a  waste  of  time,  unless,  the  designer  desire  to  check  the 
accuracy  of  his  judgment  by  comparing  the  diagram  factor,  with  diagram  factors  of  other 
similar  engines  already  built  and  operating  under  similar  conditions. 

pressure  as  it  is  called.  Accordingly,  since  the  power  developed  by  an  engine 
at  any  given  speed  is  directly  proportional  to  the  mean  effective  pressure 
actually  obtained  in  operation,  the  designer,  after  constructing  a  theo- 
retical card  for  the  working  conditions  of  initial  pressure,  cut  off,  etc., 
desired,  and  finding  the  theoretical  mean  effective  pressure  from  this  card, 
multiplies  this  by  the  diagram  factor  corresponding  to  the  type  of  engine 
being  designed.  The  value  thus  obtained  is  called  the  expected  mean 
effective  pressure^  because  the  diagram  factor,  being  obtained  by  comparing 
the  indicator  card  of  a  large  number  of  engines  of  a  similar  type  working 
under  similar  conditions  with  the  theoretical  card,  and  therefore  repre- 
senting the  allowance  which  must  be  made  for  the  various  conditions 


THE  STEAM  ENGINE 


77 


tending  to  reduce  the  theoretical  mean  effective  pressure,  gives,  as  near 
as  can  be  calculated,  the  actual  or  "expected"  mean  effective  pressure, 
when  multiplied  by  the  theoretical  mean  effective  pressure. 

Example* — The  theoretical  mean  effective  pressure  of  a  given  theo- 
retical card  is  40  lbs.  What  mean  effective  pressure  must  be  used  in  de- 
signing an  engine  to  develop  a  given  horse  power  from  the  theoretical  card 
if  the  diagram  factor  be  .85?  The  mean  effective  pressure  to  be  used  in 
obtaining  the  cylinder  dimensions,  or 

expected  M.  E.  P.  =  40  X  .85  =  34  lbs. 

It  should  be  noted  that  if  the  diagram  factor  were  disregarded  and 
40  lbs.  taken  as  the  M.  E.  P.,  then  the  actual  engine,  if  calculated  for, 
say,  100  horse  power  at  300  revolutions  per  minute,  would  develop  ap- 
proximately only 

34 

100  X  27^  =  85  horse  power 

being  100  —  85  =  15  horse  power  short  of  the  calculated  power. 

If  the  theoretical  mean  pressure  be  calculated,  and  the  necessary  cor- 
rections made  for  clearance  and  compression,  according  to  Sea  ton  the 
expected  mean  effective  pressure  may  be  found  by  multiplying  the  results 
by  the  factor  in  the  first  column  of  the  following  table : 

Diagram  Factors 


Particulars  of  Engine 

Expansive    engine,    special    valve  gear,  or    with    a 

separate  cut  off  valve,  cylinders  jacketed 

Expansive  engine  having  large  ports,  etc.,  and  good 

ordinary  valves,  cylinders  jacketed 

Expansive  engines  with  the  ordinary  valves  and  gear 

as  in  general  practice  and  unjacketed 

Compound  engines,  with  expansion  valve  to  H.  P. 

cylinder;      cylinders    jacketed,     and     with    large 

ports,  etc 

Compound    engines,    with    ordinary    slide     valves, 

cylinders  jacketed,  and  good  ports,  etc 

Compound    engines    as    in    general    practice    in  the 

merchant  service,  with  early  cut  off  in  both  cylinders 

without  jackets  and  expansion  valves 

Triple  expansion  engines,  with  ordinary  slide  valves, 

good  ports,  unjacketed,  moderate  piston  speed.  . .  . 
•Fast  running  engines  of  the  type  and  design  usually 

fitted  in  war  ships 


Diagram  Factor 


.94 

.9    to  .92 

.8    to  .85 

.9    to  .92 

.8    to  .85 

.7  to  .8 
.65  to  .7 
.6    to  .7 


.9 

.86  to  .88 

.77  to  .82 

.86  to  .88 

.77  to  .82 

.67  to  .77 
.62  to  .67 
.58  to  .67 


78  THE  STEAM  ENGINE 


If  no  correction  be  made  for  the  effects  of  clearance  and  compression, 
and  the  engine  is  in  accordance  with  general  modern  practice,  the  clearance 
and  compression  being  proportionate,  then  the  theoretical  effective  mean 
pressure  may  be  found  by  multiplying  the  results  in  the  last  column  by  .96, 
giving  the  values  in  the  second  column 

Horse  Power. — This  unit,  as  before  stated  was  introduced 
by  James  Watt  to  measure  the  power  of  his  steam  engines  and 
which  he  considered  as  being  the  power  of  a  strong  London 
draught  horse  to  do  work  for  a  short  time.  This  he  estimated 
to  be  equal  to  33,000  foot  pounds  per  minute.*  One  horse 
power  then,  or 

one  H,  P.  =33 fiOO  ft.  lbs.  per  minute 
which  is  the  accepted  standard. 

According  to  definitions,  and  the  manner  in  which  it  is  determined, 
horse  power  may  be  classed  as 

1.  Nominal  (N.  H.  P.); 

2.  Theoretical  (T.  H.  P.); 

3.  Indicated  (I.  H.  P.); 

4.  Brake  (B.H.  P.); 

5.  S.  A.  E.; 

6.  Electrical  (E.  H.  P.);  etc. 

Nominal  Horse  Power. — In  the  early  days  Watt,  according  to  Seaton, 
found  that  the  mean  pressure  usually  obtained  in  the  cylinders  of  his  engines 
was  7  lbs.  per  sq.  ins.  He  had  also  found  the  proper  piston  speed  at  128  X 
-v^stroke  per  minute,  and  his  engines  were  arranged  to  work  at  this  speed, 
so  that  he  estimated  the  power  which  would  be  developed  when  at  work  to  be 

tN.  H.  P.  =  A  X  7  X  128  X  v's' 


*NOTE. — ^James  Watt  was  early  asked  by  would  be  purchasers  as  to  how  many  horses 
his  engines  would  replace.  To  obtain  data  as  to  actual  performance  in  continuous  work,  he 
experimented  with  powerful  brewery  horses,  and  found  that  one  traveling  at  2^  m.iles  per  hour, 
or  220  feet  per  minute,  and  harnessed  to  a  rope  leadmg  over  a  pulley  and  down  a  vertical  shaft, 
could  haul  up  a  weight  averaging  100  lbs.,  equaling  22,000  foot  pounds  per  minute.  To  give 
good  measure.  Watt  increased  the  measurement  by  50  per  cent.,  thus  getting  the  familiar  unit 
of  33,000  foot  pounds  per  minute. 

tNOTE. — The  power  calculated  by  the  formula  above  was  called  "nominal,"  because 
the  engine  was  described  as  of  that  power,  and  in  practice  that  power  was  actually  obtained. 
However,  when  the  boiler  could  be  constructed  so  as  to  supply  steam  above  atmospheric 
pressure,  and  the  engine  was  run  with  more  strokes  per  minute  than  before,  the  power  developed 
exceeded  the  nominal  power,  thus  causing  the  nominal  horse  power  rating  to  be  discontinued. 


THE  STEAM  ENGINE  79 


in  which  A  =  area  of  piston  in  sq.  ins. ;    S  =  number  of  strokes  per  minute.  \ 

The  term  nominal  horse  power  is  now  obsolete  and  is  only  of  historical  \ 

interest.  : 

Indicated  horse  power. — This  is  the  actual  power  developed  by  an  engine 

as  calculated  from  the  indicator  card.    It  should  be  understood  that  it  repre-  ! 
sents  the  power  developed  at  the  instant  the  card  was  taken,  and  not 

necessarily  at  any  other  instant*.     It  should  be  carefully  noted  that  the  ; 

indicated  horse  power  of  an  engine  does  not  represent  the  power  delivered,  ] 
being  in  excess  of  the  power  delivered  by  an  amount  equal  to  the  power 

lost  by  friction  in  the  engine.  j 

Brake  Horse  Power, — By  definition,  the  actual  power  delivered  by  an  \ 

engine  as  determined  by  a  brake  test.    This  is  sometimes  called  the  delivered  \ 

horse  power ,  and  is  always  less  than  the  indicated  horse  power  by  an  amount  i 

equal  to  the  power  absorbed  by  friction  in  thfe  engine. f  \ 

S,  A,  E,  Horse  Power, — -In  order  to  reduce  all  automobile  engines  to  a  , 

common  basis  of  rating  for  determining  the  class  of  license  required,  the  j 

commissioners  of  motor  vehicles  have  adopted  a  rule  known  as  the  S.  A.  E.  '< 
horse  power  formula,  and  which  assumes  that  all  gas  engines  will  deliver 

or  should  deliver  their  rated  power  at  a  piston  speed  of  1,000  feet  per  minute,  ] 

mean  effective  pressure  of  90  lbs.  per  sq.  ins.,  and  mechanical  efficiency  \ 
of  75  per  cent.    It  should  be  understood  that  a  formula  based  on  such  data 

is  worthless  for  obtaining  the  actual  horse  power  of  an  engine  and  should  : 
only  be  used  for  the  purpose  for  which  it  is  intended. 

Electrical  Horse  Power, — It  is  desirable  to  establish  the  relation  be- 
tween watts  and  foot  pounds  in  order  to  determine  the  capacity  of  an  electric  ; 
generator  or  motor  in  terms  of  horse  power.  \ 

One  watt  is  equivalent  to  one  joule  per  second  or  60  joules  per  minute.  \ 

One  joule  in  turn,  is  equivalent  to  .7374  ft.  lbs.,  hence  60  joules  equal:  ' 

60  X  .7374  =  44.244  ft.  lbs.  i 


*XOTE. — It  should  be  understood  that  in  operation  the  power  developed  is  continually 
varying,  and,  very-  strictly  speaking,  may  be  said  never  to  be  the  same  during  any  appreciable 
interval  of  time. 

tXOTE. — The  ratio  between  the  indicated  and  brake  horse  power  of  an  engine,  that  is 
brake  horse  power  -^  indicated  horse  power  represents  the  mechanical  efficiency  of  the  engine; 
this  should  not  be  confused  with  the  thermal  efficiency,  or  heat  units  converted  into  useful 
-work  -T-  heat  units  supplied  to  the  engine. 


80 


THE  STEAM  ENGINE 


Since  one  horse  power  =  33,000  ft.  lbs.  per  minute,  the  electrical  equiv- 
alent of  one  horse  power  is 

33,000  -^  44.244  =  746  watts. 
or, 


746 
1,000 


=  .746  kilowatts  (K.  W.) 


Again,  one  kilowatt  or  1,000  watts  is  equivalent  to 
1,000  -^  746  =  1.34  horse  power. 


Fig.  89. — Diagram  illustrating  why  the  decimal  .7854  is  used  to  find  the  area  of  a  circle.  If 
the  square  be  divided  into  10,000  parts  or  small  squares,  a  circle  having  a  diameter  D,  equal 
to  a  side  of  the  large  square  will  contain  7854  small  squares,  hence,  if  the  area  of  the  large 
square  be  1  sq.  in.,  then  the  area  of  the  circle  will  be  7854^10,000  or  .7854  sq.  ins.,  that  is, 
area  of  the  circle  =.7854  XD2  =.7854  XD  XD  =.7854  XI  XI  =^.7854  sq.  ins. 


How  to  Calculate  Horse  Power. — There  are  various  formulas 
for  calculating  the  power  of  engines,  and  the  student  should 
endeavor  to  understand  the  principles  upon  which  they  are 
based  rather  than  simply  committing  them  to  memory.  Before 
taking  up  these  formulae  a  few  preliminary  considerations  are 
necessary. 


Oues.    Why  is  the  decimal  .7854  used  to  ascertain  the 
area  of  a  circle  or  piston? 


THE  STEAM  ENGINE  81     ? 


Ans.  Because  it  represents  the  relation  between  a  circle 
and  circumscribed  square. 

This  relation  is  clearly  shown  in  fig.  89. 

Oues.     What  is  understood  by  the  term  piston  speed? 

Ans.  It  is  the  total  distance  traveled  by  the  piston  of  an 
engine  in  one  minute — not  the  actual  velocity  at  any  given 
instant  of  time. 

Ones.     How  is  the  piston  speed  obtained? 

Ans.  RULE:  Multiply  twice  the  number  of  revolutions  per 
minute  by  the  stroke  of  the  engine  in  inches  and  divide  the 
product  by  12  to  reduce  to  feet. 

Thus,  an  engine  having  a  stroke  of  6  inches  and  running  500  revolutions 
per  minute  is  said  to  have  a  piston  speed  of 

.2X6X500. 


12 


=  500  feet  per  minute. 


Oues.  What  is  the  usual  method  of  calculating  the 
horse  power  of  an  engine? 

Ans*  RULE:  Multiply  the  mean  effective  pressure  i^i  lbs.  per 
square  inch  by  the  area  of  piston  in  square  inches  and  multiply  the 
product  by  the  length  of  stroke  in  feet,  and  by  the  number  of  strokes 
per  minute  {twice  the  number  of  revolutions) ;  divide  this  last  product 
by  33,000  and  the  answer  will  be  the  horse  power  for  a  double 
acting  engine. 

This  method  which  is  very  generally  used  is  expressed  as  a  formula  as 
follows : 

jj  p  _2XPXLXAXN  _2(.7854D2)PLN  .^. 

33,000  ~  33,000  


NOTE. — Horse  power  expressed  in  thermal  units. — Since  1  B.  t.  u.  is  equivalent  to 
777.52  ft.  lbs.  (Marks  and  Davis),  and  one  horse  power  =  33,000  ft.  lbs.  per  minute,  then 
one  horse  power  =  33,000  -r-  777.52  =  42.44  B.  t.  u.  per  minute. 


82  THE  STEAM  ENGINE 


in  which 

P=mean  effective  pressure  in  lbs.  per  sq.  ins.; 

L  =  length  of  stroke  in  feet; 

A  =  area  of  piston  in  sq.  ins.  =  . 7854 X diameter  of  piston  squared; 

N  =  number  of  revolutions  per  minute ; 

D  =  diameter  of  piston. 

It  should  be  noted  that  the  numerator  represents  the  total  ft.  lbs.  done 
by  the  engine  in  one  minute;  the  figure  2  is  introduced  because  in  the  double 
acting  engine  there  are  two  power  strokes  each  revolution.  The  denomi- 
nator or  33,000  is  the  foot  pounds  per  one  minute  for  one  horse  power. 

Example. — What  is  the  horse  power  of  a  5X6  engine  running  at  500 
revolutions  per  minute  and  50  lbs.  mean  effective  pressure? 

Substituting  these  values  in  the  formula,  and  remembering  that  the 
area  A  of  the  piston  =  .  7854  X  its  diameter  squared, 

2X  (.7854X52)  X50Xr2X500 

H.  P.  = : =  14.87 

33,000 

Oues.  What  is  the  objection  to  the  formula  just 
given? 

Ans.  It  involves  a  considerable  waste  of  time  in  making  the 
calculation. 

Since  the  stroke  of  an  engine  is  usually  given  in  inches  instead  of  feet, 
and  the  revolutions  per  minute  instead  of  the  piston  speed,  the  formula 
just  given  evidently  involves  extra  calculations  for  these  items  as  well  as 
the  extra  multiplication  and  division  introduced  because  of  the  constants. 
Its  use  therefore  is  about  as  laborious  as  multiplying  and  dividing  fractions 
without  reducing  them  to  their  lowest  terms. 

The  author  strongly  recommends  that  the  formula  just  given  be  not  used 
in  the  form  given  but  reduced  to  its  lowest  terms  as  follows : 

2PLAN     2XPX  i^X.7854XD2xN     .1309XPLD2N 

H.  P.= = L2 ^ . 

33,000  33,000  33.000 

=  .00000396  7  PLD2N 

Using  the  constant  .000004  instead  of  .000003966  v^hich  is 
near  enough  for  ordinary  calculations,  and  changing  the  order 
of  the  factors,  the  formula  becomes 

H.  P. =. 000004  D^LNP    .    .    .  (2) 


THE  STEAM  ENGINE 


83 


Example, — What  is  the  horse  power  of  the  engine  in  the  previous 
example  (running  under  the  same  conditions),  as  calculated  by  formula  (2)? 
Substituting  the  given  value  in  (2) 

H.  P.  =.000004X52X6X500X50  =  15 

Comparing  the  two  formulae,  15  h.  p.  is  here  obtained  instead  of  14.87, 
the  error  introduced  by  using  the  constant  .000004  instead  of  .000003966, 
being  only 

86 
15  —  14.8/  =.13  horse  power  or  tTvt:  of  1% 

This  short  formula  (2)  is  very  valuable  to  those  who  have  frequent 
occasions  to  calculate  horse  power.  The  power  of  any  engine  on  a  basis  of 
of  500  revolutions  and  50  lbs.  mean  effective  pressure  can  be  very  quickl}^ 


Fig.  90. — View  of  Buffalo  small  vertical  piston  valve  stationary  engine.  The  main  bearings 
are  ring  oiling  and  receive  their  supply  of  lubrication  from  the  bed  by  the  rotation  of  the 
crank  disk;  they  are  carried  on  a  heavy  plate  bolted  to  the  frame.  Removable  heads  sur- 
mounting them  shut  out  all  ^he  dust  and  grit  and  allow  of  ready  access  for  adjustment.  A 
false  head  forms  a  chamber  to  prevent  condensation  getting  into  the  engine  bed.  This  is  a 
so  called  "square"  engine,  that  is  the  stroke  is  the  same  length  as  the  piston  diameter.  The 
5  X  ■>  size  at  475  r.  p.  m.  is  rated  at  12  horse  power,  and  the  6  X  6  at  450  r.  p.  m.,  18  horse 
power.    Compare  these  ratings  with  the  5X6  engine  given  in  the  example  on  page  82. 


84  THE  STEAM  ENGINE 

found  with  this  formula  and*  the  method  of  using  it,  as  given  below,  will 
firmly  fix  it  in  mind,  though  as  before  stated,  the  author  does  not  recommend 
memorizing  formulae  but  instead,  the  acquirement  of  a  knowledge  of 
principles  upon  which  they  depend. 

Now,  for  a  quick  calculation  of  the  horse  power  of  the  engine  in  the 
previous  example, 

1.  Write  down  the  cylinder  dimensions,  squaring  the  diameter 

(52X6) 

2.  Disregard  the  decimal  point  and  write  4  instead  of  .000004 

4  X  (52X6) 

3.  Insert  the  revolutions  per  minute  and  the  mean  effective  pressure 

4X(52X6)X500X50 

The  product  of  these  factors  is  the  horse  power  when  the  decimal  point  is  inserted 
in  the  right  place. 

4.  Since  the  product  of  the  first  and  last  two  factors  is  100,000,  dis- 
regarding the  ciphers,  only  the  factors  inside  the  parenthesis  need  be  con- 
sidered to  obtain  the  horse  power,  thus 

52X6  =  5X5X6  =  150 (3) 

It  remains  only  to  insert  the  decimal  point,  which  is  determined  from  the 
sense  of  proportion ,  that  is,  any  one  familiar  with  engines  would  know  that 
a  0X6  engine  running  at  500  R.  P.  M.  and  50  lbs.  mean  effective  pressure 
does  not  develop  150  h.  p.  as  written  in  equation  (3);  neither  does  it 
develop  only  1.5  h.  p.;  it  must  then  develop  15  h.  p. 

From  the  foregoing  it  must  be  evident  that  to  obtain  the 
horse  power  of  any  engine  running  at  500  revolutions  per  minute 
and  50  lbs.  mean  effective  pressure  it  is  only  necessary  to  consider 
the  dimensions  of  the  cylinder  and  to  point  off  one  place,  or 
multiply  by    .1  as  expressed  in  the  following  formula, 

H.  P.  =  .l  X  diameter  piston 2  x  stroke  .   .  (4) 
diameter  and  stroke  being  taken  in  inches.     Expressed  as  .a 
rule  the  formula  becomes: 

Rule. — For  500  revohitions  per  minute,  and  50  Ihs.  per  sq,  in, 
M.  E.  P.y  square  the  diameter  and  multiply  by  the  stroke,  both  in 
inches;    multiply  the  product  by  .1,  that  is,  point  off  one  place. 

Ones.  How  is  the  horse  power  obtained  by  (4)  for 
other  than  500  R.  P.  M.  and  50  lbs.  M.  E.  P.? 


THE  STEAM  ENGINE 


Ans.  By  multiplying  the  result  obtained  in  (4)  by  the  ratio 
between  the  given  R.  P.  M.  and  500,  and  the  given  M.  E.  P. 
and  50. 


Expressed  as  a  formula  (4)  becomes 
H.  P.  =  (h.p.  at  500  r.  p.  m.  and  50  lbs.  m.  e.  p.)  X?^-^^  X^i^^  .     (5) 


500 


50 


Return  SfroAe 


Fig.  91. — Working  principles  of  the  indicator.  In  the  figure,  A,  is  a  small  cylinder  screwed  into 
the  engine  cylinder  and  opening  into  the  clearance  space  B.  C,  is  a  piston  working  within  A, 
against  the  pressure  of  the  steam  in  B,  by  means  of  the  tension  of  the  spring  D.  E,  is  a 
horizontal  arm  attached  to  the  rod  of  the  piston  C,  and  carrying  on  its  outer  end  a  pencil 
point  F.  G,  is  a  carrier  bar  upon  which  a  board  H,  carrying  a  sheet  of  paper  is  moved  back 
and  forth  in  a  direction  opposite  to  that  of  the  piston  of  the  engine,  by  means  of  the  spring 
L,  and  the  lever  M,  the  upper  end  of  the  latter  being  attached  by  a  cord  to  the  movable 
board  and  the  lower  end  to  some  part  of  the  piston  rod  such  as  the  crosshead  N.  In  oper- 
ation,  assume  the  piston  K,  to  be  at  its  inner  dead  center  o,  and  the  clearance  space  B,  to  be 
empty.  The  piston  C,  will  be  down,  and  pencil  point  at  F.  Now,  if  steam  be  admitted  to  B, 
the  increasing  pressure  will  drive  the  piston  C,  upward,  carrying  the  pencil  vertically  from 
F,  to  r,  until  the  pressure  in  the  clearance  space  is  sufficient  to  move  the  piston.  If  this  pressure 
be  kept  constant  while  the  piston  travels  from  o,  to  p,  and  moves  the  board  H,  through  a 
corresponding  distance  from  o',  to  p',  the  pencil  will  trace  the  line  r  x.  But  ordinarily,  the 
pressure  is  not  kept  constant,  the  supply  of  steam  being  stopped  when  the  piston  has 
traveled  some  part  of  its  forward  stroke.  Assume  that  the  supply  of  steam  be  stopped  when 
the  piston  has  traveled  a  distance  equal  to  one-quarter  the  length  of  its  full  stroke,  or  to  c. 
The  movement  of  the  piston  from  o,  to  z  will  carry  the  board  from  o',  to  z',  and  as  the  pressure 
is  kept  constant  up  to  this  point,  the  pencil  will  trace  a  horizontal  line  from  r,  to  s,  the  cut  off 
point.  The  continued  advance  of  the  piston  will  move  the  board  towards  p\  and  as  it  will 
also  increase  the  volume  of  the  steam,  the  pressure  in  the  engine  cylinder  will  fall,  thus 
relieving  the  compression  on  the  spring  D,  and  alio  wing  the  piston  C,  to  descend.  As  the  result 
of  these  operations  and  movements,  the  indicator  pencil  will  trace  the  line  5  /,  the  point  t 
coinciding  with  the  point  F,  on  the  diagram  when  the  piston  is  at  its  outer  dead  center  p, 
and  the  board  at  the  limit  of  its  backward  movement  p'.  Driven  by  the  stored  up  energy 
in  the  fly  wheel,  the  engine  piston  will  travel  from  p,  to  o,  on  its  return  stroke,  pulling  the 


86  THE  STEAM  ENGINE 


Example,— K  5X6  engine  at  500  R.  P.  M.  and  50  lbs.  M.  E.  P.  develops 
15  horse  power.    What  will  be  the  power  at 

1.  250  R.  P.  M.  and  50  M.  E.  P.? 

2.  500  R.  P.  M.  and  40  M.  E.  P.? 

3.  400  R.  P.  M.  and  60  M.  E.  P.? 

The  factor  in  the  parenthesis  of  formula  (5)  being  given  in  the  example 
as  15,  the  powers  developed  corresponding  to  the  above  running  conditions 
are 

1.H.P.^15X||X^J  =  7^. 

2.  H.  P.  =  15x55?X-  =  ^  =  12. 

500     50      5 

3.  H.P.  =  15x|^X^  =  ^><i><-^  =  14.4, 

500     50  5 

This  method  is  useful  for  mental  calculation. 

Expressed  as  rules,  the  two  principles  upon  which  the  above  calculations 
are  based  are : 

Rule. — At  constant  speed,  the  horse  power  of  an  engine  varies  directly  as 
the  mean  effective  pressure. 

Rule. — At  constant  mean  effective  pressure,  the  horse  power  of  an  engine 
varies  directly  as  the  speed. 

Oues.     Give  a  very  short  rule  for  finding  the  horse  power 
of  a  single  cylinder  engine. 

Ans.     Square  the  piston  diameter  and  divide  by  2. 


Fig.  91. — Continued. 

board  from  p'  to  q',  and  as  no  pressure  exists  in  the  cylinder,  the  indicator  piston  will  remain 
down,  and  the  indicator  pencil  will  trace  the  line  t  F,  and  thus  complete  the  diagram, 
the  area  of  which  graphically  represents  the  work  done  by  the  engine  per  rev.  It  should 
be  noted  that  for  simplicity,  pre-release  and  excess  back  pressure  are  not  considered, 
steam  being  assumed  to  expand  to  the  pressure  of  exhaust  at  t.  In  actual  indicators, 
the  pencil  arm  E,  referred  to,  instead  of  being  attached  in  a  fixed  horizontal  position  to  the 
upper  end  of  the  rod  of  the  indicator  piston  is  replaced  by  a  system  of  levers  which  multiplies 
the  motion  of  the  piston,  thus  permitting  the  use  of  indicator  cylinders  whose  pistons  have 
a  smaller  range  of  motion.  Also,  the  movable  board  H,  is  replaced  by  a  rotatable  drum 
which  carries  the  paper.  A  spiral  spring  in  the  interior  of  the  drum  rotates  it  in  a  direction 
opposite  to  that  of  the  forward  stroke  of  the  engine  piston ,  the  spring  being  put  into  a  state 
of  tension,  when  the  drum  is  rotated  in  the  opposite  direction,  by  means  of  a  cord  attached 
to  the  engine  piston,  during  the  return  stroke  of  the  latter.  These  substitutions  allow  very 
compact  and  efficient  mechanical  arrangements. 


THE  STEAM  ENGINE 


This  is  correct  whenever  the  product  of  mean  effective  pressure  and  piston 
speed  =  21,000,  as  in  the  following  combinations: 


Mean  effective  pressure 

30 

35 

38.2 

(Approx.) 

42 

Piston  speed 

700 

600 

550 

500 

I   i   I   I 

I  I  I  I 


I    I    i    M    I    I 

/I   /I    -1   /I   /I  /I  /\   //;"■ 

H./  /  I  i  !    i 


•^•^. 


/ 


Fig.  92. — Indicator  card  showing  method  of  finding  M.  E.  P.  by  summation  of  ordinates. 

First  two  Hnes  are  drawn  perpendicular  to  the  atmospheric  line  and  touching  the  cards  at 
the  ends  as  shown.  On  a  slanting  line  starting  at  the  intersection  A,  of  the  atmospheric  line 
and  the  vertical  line,  a  scale  is  constructed  that  helps  to  find  the  desired  ten  subdivisions 
on  the  length  of  the  diagram,  and  on  which  the  mean  height  of  each  tenth  is  to  be  measured. 
The  scale  on  the  slanting  line,  starting  from  the  point  of  intersection  A,  may  be  made  by 
setting  off,  first  ]4  inch,  then,  nine  3^  inch  spaces,  and,  finally,  again  ^  inch,  thus  making 
the  whole  scale  five  inches  long.  The  end  point,  B,  of  this  scale  is  connected  by  a  straight 
line  with  the  intersection  C,  of  the  atmospheric  line,  and  the  second  vertical  line,  and  lines 
parallel  to  B  C,  are  drawn  through  all  the  other  ten  points  of  the  scale,  to  intersect 
with  the  atmospheric  line.  After  drawing  vertical  lines  through  all  these  intersecting  points, 
the  ten  mean  ordinates,  or  pressures,  can  be  measured,  each  individually,  or  in  a  convenient 
way,  as  a  sum  total,  by  taking  off  all  the  ordinate  continuously  upon  a  strip  of  paper. 
If  this  sum  total  be  divided  by  ten,  the  mean  ordinates  for  the  whole  diagram  is  found.  To 
find  the  M.  E.  P.,  muUipLy  the  mean  ordinate  by  the  scale  of  spring. 

Horse  Power  Constant. — If  it  be  desired  to  make  a  number 
of  horse  power  calculations  of  a  given  engine  under  different 
nditions   of  speed  and  mean   effective  pressure  to   show  its 


THE  STEAM  ENGINE 


power  range,  it  must  be  evident,  that  it  would  be  a  waste  of  time 
to  multiply  the  constants  such  as  piston  diameter,  stroke, 
.000004,  etc.,  for  each  calculation.  Accordingly,  if  all  these 
constants  be  multiplied,  a  value  is  obtained  which  is  called  the 
horse  power  constant,  and  to  obtain  the  horse  power  in  each 
case,  it  is  only  necessary  to  multiply  the  horse  power  constant 
by  the  variable  quantity  or  quantities. 

Example. — What  is  the  horse  power  constant  of  a  5X6  engine  using  the 
formula  H.  P.  =.000004  D^  L  N  P.  Here  .000004;  D,  diameter  =  5,  and  L, 
stroke  =  6  do  not  vary,  while  N  and  P  are  variables  hence 

horse  power  constant  =  .000004  XS^XG  =  .0006 
from  which  the  horse  power  of  this  engine  at  say  500  R.  P.  M.  and  50    ibs. 


M.  E.  P.  is 


.0006X500X50  =  15 


The  horse  power  constant  as  just  found  is  useful  where  both  N  and  P, 
the  revolutions  and  mean  effective  pressure  are  considered  as  "variables." 
However,  in  making  a  ''horse  power  table"  for  a  given  engine  several  sets 
of  calculations  are  made  for  a  constant  value  of  N  or  P.  That  is  regarding 
N  as  constant,  the  horse  power  constant  would  be 

.000004  D2  L  P (1) 

or,  regarding  P  as  constant,  the  horse  power  constant  becomes 

.000004  D2  L  N (2) 

The  following  examples  show  the  application. 

Example. — Calculate  the  horse  power  of  a  5X6  engine  at  30  lbs.  mean 
effective  pressure  for  speeds  of  100,  200,  300,  400,  and  500  revolutions  per 
minute. 

In  this  case  the  horse  power  constant  is  as  expressed  in  (1)  and  its  value  is 
.000004X5^X6X30  =  .018 
from  which:  for  100  r.  p.  m.,  h.  p.  =.018X100  =  1.8;  for  200  r.  p.  m.,  h.  p.  = 
.018X200  =  3.6;   for  300  r.  p.  m.,  h.  p.  =.018X300  =  5.4;   for   400  r.  p.  m., 
h.  p.  =  .018X400  =  7.2;  for  500  r.  p.  m,  h.  p.  =  .018X500  =  9. 

Example. — Calculate  the  horse  power  of  the  engine  in  the  preceding 
example  at  500  revolutions  per  minute  for  mean  effective  pressures  of  40, 
50  and  60  lbs.  per  sq.  in. 

Here,  the  horse  power  constant  is  as  expressed  in  (2),  and  its  value  is 
.000004X52X6X500  =  .3 
from  which:   for  40  m.  e.  p.,  h.  p.  =.3X40  =  12;   for  50  m.  e.  p.,  h.  p.  = 
.3X50  =  15;   for  60  m.  e.  p.,  h.  p.  =.3X60  =  18.    The  results  obtained  are 
tabulated  as  follows: 


THE  STEAM  ENGINE 


Table  of  Horse  Power  Constants 

For  formula  H.P.  =.000004D^LNP;  con«f an*  =.000004D^LP 


Size  of 
cylinder 
(inches) 

Mean  effective 

pressure 

25 

30 

35 

40 

oU 

OU         V,) 

IX  1 

.0001 

.00012 

. 00014 

. 00016 

.0002 

. 00024 

.0003 

2X  2}4 

.001 

.0012 

.0014 

.0016 

.002 

.0024 

.003 

3X  3 

.0027 

. 00324 

. 00378 

. 00432 

.0054 

.00648 

.0081 

3X  4 

.0036 

. 00432 

. 00504 

. 00576 

.0072 

. 00864 

.0108 

4X  4 

.0064 

. 00768 

.00896 

.01024 

.0128 

.01536 

.0192 

oX  5 

.0125 

.015 

.0175 

.02 

.025 

.03 

.0375 

5X  6 

.015 

.018 

.021 

.024 

.03 

.036 

.045 

6X  6 

.0216 

. 02592 

.0324 

. 03456 

.0432 

.05184 

.0648 

7X  7 

.0343 

.04116 

. 04802 

. 05488 

.0686 

. 08232 

.1029 

7X  9 

.0441 

. 05292 

.06174 

. 07056 

.0882 

. 10584 

.1323 

8X  8 

.0512 

.06144 

.07168 

.08192 

.1024 

. 1628S 

.1536 

8X  10 

.064 

.0768 

.0896 

.1024 

.128 

.1536 

.192 

9X9 

.0729 

. 08748 

. 10206 

. 13464 

.1458 

• . 17496 

.2187 

9  X  12 

.0972 

.1164 

. 13608 

. 15542 

.1844 

.2328 

.2916 

10  X  12 

.12 

.144 

.168 

.192 

.24 

.288 

.36 

11  X  14 

.1694 

. 20328 

.23716 

. 27104 

.3388 

. 40656 

.5082 

12  X  12 

.1728 

. 20736 

.24182 

. 27648 

.3456 

.41472 

.5184 

13  X  13 

.2197 

. 26364 

. 30758 

.35152 

. 52728 

. 92728 

.  6.591 

14  X  14 

.2744 

. 32828 

.38316 

. 43804 

.5488 

. 65656 

.8232 

15  X  15 

.  3375 

.405 

.4725 

.54 

.675 

.81 

1.0125 

16  X  16 

.4096 

. 49052 

. 57344 

. 65536 

.8192 

. 98104 

1.2288 

18  X  18 

.5832 

. 69984 

.81648 

.93312 

1.16640 

1.39968 

1.7496 

20  X  24 

.96 

1.152 

1.344 

1.536 

1.92 

2.304 

2.88 

22X26 

1.2584 

1.51008 

1.66176 

2.01344 

2.5168 

3.02016 

3.7752 

24  X  30 

1.728 

2.0736 

2.4192 

2. 7648 

3.456 

4. 1472 

5.184 

Cor  Hi  8  iizes 

10X24 

.24 

.288 

.336 

.384 

.48 

.576 

.72 

12X24 

.3456 

.41472 

. 48384 

. 55296 

.6912 

. 82944 

1.0368 

12X30 

.432 

.5184 

.6048 

.6912 

.864 

1.0368 

1.296 

14  X  30 

.588 

.7056 

.8232 

.9408 

1.176 

1.4112 

1.764 

14X36 

.7056 

. 84672 

. 98784 

1.12896 

1.4112 

1.69344 

2.1168 

16  X  30 

.768 

.9216 

1.0752 

1.2288 

1.536 

1.8432 

2.304 

16X36 

.9216 

1.10592 

1.29024 

1.47456 

1.8432 

2.21184 

2.7648 

16X42 

1.0752 

1.29024 

1.50528 

1.70232 

2.1504 

2.58048 

3. 2256 

18X36 

1.1663 

1.39936 

1.73282 

1.86608 

3.33261 

2.79872 

3.49892 

18X42 

1.3608 

1.63296 

1.90512 

2. 17728 

2.7216 

3. 26592 

4.0818 

20X36 

1.44 

'1.728 

2.016 

2.304 

2.88 

3.456 

4.32 

20X42 

1.68 

2.016 

2.352 

2.688 

3.36 

4.032 

5.04 

20X48 

1.92 

2.304 

2.688 

3.072 

3.84 

4.608 

5.76 

22  X  42 

2.  0328 

2. 43936 

2. 84592 

3.25248 

4.0656 

4. 87872 

6.0984 

22X48 

2.3232 

2. 78784 

3. 25048 

3.71712 

4.6464 

5. 57568 

6.9696 

22X54 

2.6136 

3. 13632 

3.65904 

4.18176 

5. 2272 

6. 27204 

7. 8408 

24X42 

2.41919 

2.90303 

3.38687 

3.8707 

4.83838 

5. 80606 

7.25757 

24X48 

2.7648 

3.31776 

3.78072 

4.42368 

5.5296 

6. 63552 

8. 2944 

24  X  54 

3. 1104 

3.73248 

4. 35456 

4.97664 

6. 2208 

7.46496 

9.3312 

26X48 

3.24471 

3.89365 

4.54259 

5. 19153 

6.48942 

7.78731 

9.73413 

26  X  54 

3. 6504 

4.38048 

5.11056 

5. 84064 

7.3008 

8. 76096 

10.9512 

26X60 

4.056 

4.8672 

5.6784 

6.  4896 

8.112 

9.7344 

12. 168 

28  X  48 

3.  7632 

4.50584 

5.26848 

6.02112 

7.5264 

9.01168 

11.2896 

28X54 

4.2336 

5.08032 

5.92704 

6.77376 

8. 4672 

10. 16064 

12.7008 

28X60 

4.704 

5.  6448 

6. 5856 

7. 5264 

9.408 

11.2896 

14.112 

30X48 

4.32 

5.184 

6.048 

6.912   . 

8.64 

10. 368 

12.96 

30  X  54 

4.86 

5.832 

6.804 

7.776 

9.72 

11.696 

14.58 

30  X  60 

5.4 

6.48 

7.56 

8.64 

10.8 

12.96 

16.2 

32X48 

4.9152 

5. 89824 

6.  88128 

7.86432 

9.8304 

11.79648 

14.7456 

32X54 

5.5296 

6. 63552 

7.74144 

8.84736 

11.0592 

13.^7104 

16. 5888 

32X60 

6.144 

7.33728 

8.56026 

9.78304 

12. 288 

14.67556 

18.432 

34X54 

6.  24241 

7.49089 

8. 73937 

9.98785 

12.48482 

14.98178 

18.72723 

34X60 

6.935 

8.3132 

9.7104 

11.0976 

13.  87 

16. 6264 

20. 805 

90 


THE  STEAM  ENGINE 


Horse  Power  Table 

M.  E.  P. 

Revolutions  per  minute 

100 

200 

300 

400 

500 

30 

1.8 

3.6 

4.6 

7.2 

9 

40 

2.4 

4.8 

7.2 

9.6 

12 

50 

3 

6 

9 

12 

15 

60 

3.6 

7.2 

10.8 

14.4 

18 

The  values  in  heavy  figures  are  those  obtained  in  the  two  examples, 
the  other  values  are  obtained  by  similar  calculations,  or  by  a  shorter 
process  by  applying  the  rule  for  variable  speed  as  given  on  page  86. 
Thus,  having  found  the  value  2.4  h.  p.  for  100  r  p.  m.  and  40  lbs.  m.  e.  p., 
the  other  values  for  40  lbs.  m.  e.  p.  would  'be,  applying  the  rule,  2.4X2  = 
4.8  h.  p.  for  200  r.  p.  m.;  2.4X3=7.2  h.  p.  for  300  r.  p.  m.,  etc. 

Oues.  For  great  accuracy,  what  should  be  considered 
in  addition  to  the  factors  included  in  the  horse  power 
formulae  already  given? 

Ans.     The  cross  sectional  area  of  the  piston  rod. 

Oues.     Why? 

Ans.  Because  it  reduces  by  a  small  amount  the  power  in- 
dicated by  the  formulae. 

Effect  of  the  Piston  Rod  oh  the  Power. — It  must  be  evident 
since  the  piston  rod  passes  through  the  stuffing  box  in  the 
cylinder  head,  that  the  area  of  the  piston  tipon  which  steam  acts 
at  this  end  is  reduced  by  an  amount  equal  to  the  cross  sectional 
area  of  the  rod,  whereas,  on  the  other  side  of  the  piston  steam 
acts  on  its  entire  area.  Accordingly  the  power  developed  at  the 
* 'crank  end"  will  be  less  than  at  the  ''head  end."* 

Since  this  reduction  of  power  is  so  small  and  the  range  of  power 
of    a    steam    engine    so    great,    this    ordinarily    need    not    be 


*NOTE. — The  terms  crank  end  and  liead  end,  mean  respectively  the  end  nearest  or  farthest 
from  the  crank  or  shaft. 


THE  STEAM  ENGINE 


91 


considered,  and  in  most  cases  the  extra  calculation  is  a  waste  of 
time,  however,  it  is  important  that  the  principle  involved  he 
understood. 


Fig.  93. — Sectional  diagram  of  the  indicator.  A,  is  the  swinging  bar;  B,  the  pencil  bar;  C,  the 
indicator  frame;  D,  cylinder  containing  tension  spring;  E,  coiled  spring  on  drum  roller;  F, 
revolving  cylinder  or  drum;  G,  drum  pin;  H  and  Z,  thumb  screws  holding  drum;  1,  nut  to 
connect  indicator  to  pipe;  K,  lever  for  screwing  up  I;  M,  connection  between  the  spring 
cylinder  and  pipe;  P,  piston  rod;  R,  joint;  S,  pin;  T,  post  for  guide  of  pencil  bar;  V,  guide 
pulley  for  cord  from  reducing  lever;  W,  swivel  sleeve  for  cord;  X,  swivel  pin;  Y,  support  for 
swivel  pin. 


92 


THE  STEAM  ENGINE 


To  simplify  the  calculation,  the  average  effect  is  considered, 
that  is,  half  the  piston  rod  area  is  regarded  as  being  removed 
from  each  face  of  the  piston,  instead  of  the  full  area  from  one 
face  only.  The  following  example  will  illustrate  the  methods 
of  calculation. 

Example* — A  5X6  engine  running  at  50  lbs.  m.  e.  p.,  and  500  r.  p.  m. 
develops  15  horse  power,  neglecting  the  effect  of  the  piston  rod.  What 
power  is  developed,  considering  a  piston  rod  1  inch  in  diameter? 


Fig.  94. — One  form  of  reducing  lever  for  an  indicator  attachment.  A,  is  attachment  of  the  cord ; 
B,  end  of  cord;  C,  pivot  of  reducing  lever;  D,  swinging  joint  of  reducing  lever;  E,  point  of 
attachment  to  cross- head  for  the  link  joining  reducing  lever  at  D.  The  indicator  is  shown  at 
top  of  cylinder,  connected  by  a  three-way  cock  to  pipes  from  both  ends  of  cylinder. 

1st  Solution, 

From  table,  or  by  calculation,  area  5"  piston  =  19.635;  area  cross  section  1" 
piston  rod  =  .7854;  3^  piston  rod  area  =  . 7854 -r- 2  =  .3927  sq.  ins.  1  %  of 
piston  area  =  19. 635 X. 01  =.197,  hence  j^  piston  rod  area  =  .3927 -i- 
.197  =  .0199,  that  is  1 .99%  of  piston  area.  Accordingly  the  power  is  reduced 
1.99%,  or  15 X. 0199  =  .299  horse  power,  from  which  the  actual  power 
of  the  engine  is  15  —  .299  =  14.7  horse  power. 

2d  Solution. 

Area     5''     piston  =  i/4V  D2  =  .7854X52  =  .7854X5X5  =  19.635 
Similarly,  or  from  table,  3^  area  of  1''  piston  rod  =  .3927. 

Effective    piston    area  =  19.635  —  .3927  =  19.2423,    say    19.24    sq.    ins. 

Now,  area  of  piston  =  .7854D2,  from  which  D2  =  area  of  piston -t-. 7854, 
or   D=  Varea    of   piston    X    .7854=  Vi9;24T?7854=  V24.497=4.95 


sq. 


THE  STEAM  ENGINE 


93 


Substituting,  this  value  of  D,  and  the  stroke  in  formula  (4)  (page  84)  for 
horse  power  of  an  engine  running  at  50  lbs.  m.  e.  p.  and  500  r.  p.  m., 

H.P.  =  . 1X4.952X6  =  14.7 

Brake  Horse  Power. — This  is  the  useful  horse  power  de- 
livered by  an  engine  as  ascertained  by  the  application  of  a  brake 
or  absorption  dynamometer.  The  excess  of  the  indicated 
horse  power  over  that  required  by  the  brake,  represents  the  power 
required  to  move  the  engine  in  overcoming  its  friction. 


Fig.  95. — Prony  brake.  It  consists  of  a  friction  band  which  may  be  placed  around  the  fly 
wheel  or  the  crank  shaft,  and  attached  to  a  lever  bearing  upon  the  platform  of  a  weighing 
scale,  as  shown.  A  brake  used  for  testing  purposes  should  be  self-adjusting  to  a  certain 
extent,  so  as  to  maintain,  automatically,  a  constant  resistance  at  the  rim  of  the  wheel.  For 
comparatively  small  engines,  various  forms  of  rope  brake,  satisfy  this  requirement  very  well. 
In  such  cases,  a  weight  is  hung  to  one  end  of  the  rope  and  a  spring  scale  to  the  other  end. 
I  The  wheel  should  be  provided  with  interior  flanges,  holding  water  for  keeping  the  rim  cool. 
For  very  high  speeds,  some  form  of  water  friction  brake  should  be  employed,  as  they  have 
the  advantage  of  being  self-cooling. 


The  power  of  small  engines  running  at  very  high  speeds,  is 
best  obtained  by  a  brake  test,  since  indicator  cards  become 
disturbed  under  such  conditions,  thereby  introducing  errors. 
The  form  of  absorption  dynamometer  generally  used'  for  ob- 
taining brake  horse  power  is  called  the  Prony  brake  (named 
after  its  inventor).     Its  construction  is  shown  in  fig.  95. 


94  '      THE  STEAM  ENGINE 

Formula  for  Brake  Horse  Power. — The  net  work  of  the 
engine  or  horse  power  delivered  at  the  shaft  is  determined  as 
follows : 

Let  W  =  power  absorbed  per  minute; 

P  =  unbalanced  pressure  or  weight  in  pounds,  acting  on  the  lever  arm 
at  a  distance  L; 

L=  length  of  lever  arm  in  feet  from  center  of  shaft; 

N  =  number  of  revolutions  per  minute; 

V  =  velocity  of  a  point  in  feet  per  minute  at  distance  L,  if  arm  were  allowed 
to  rotate  at  the  speed  of  the  shaft  =  2  tt  L  N 

P  \' 

Since  brake  horse  power  = 

^  33,000 

substituting  for  V, 

B.H.  P.  (brake  horse  power)  =2  tt  L  N  P ^^ 

33,000 
It  should  be  noted  that  if  L=33-^2  tt  the  equation  becomes 

B.  H.  P.  =  -^^X  — X  N  P  =  ii^ (2) 

33,000     27r  1,000 

Accordingly,  in  order  to  use  the  simplified  formula  (2)  the  arm  L  is 
made  33-j-27r  or  5.285  feet,  very  approximately  5  ft.  3]Y6  inches. 

Oues.  What  important  precaution  should  be  taken  in 
making  a  brake  test? 

Ans.  The  lever  arm  L,  should  be  horizontal  when  a  weight 
is  used  so  that  the  force  due  to  gravity  will  act  at  right  angles 
to  the  arm. 

4 

If  the  arm  he  in  any  other  position,  the  effect  will  he  the  same  as  shortening 
the  arm  and  will  introduce  an  error  in  the  calculation. 

Size  of  Cylinder.— Having  learned  the  principles  and  methods 
of  calculating  the  horse  power  of  an  engine,  as  given  in  the 
preceding  pages,  the  student  should  now  consider  how  to  cal- 
culate the  diameter  and  stroke  of  an  engine  to  develop  a  given 
horse  power. 


THE  STEAM  ENGINE 


95 


It  must  be  evident  that  for,  say,  a  given  speed,  a  great  many 
cylinder  sizes  could  be  used,  each  giving  the  same  power,  that 
is,  a  long  stroke  with  small  piston,  or  a  large  piston  with  small 
stroke  could  be  used,  the  best  proportion  between  the  stroke 
and  diameter  being  determined  by  the  type  of  engine,  service 
for  which  it  is  intended,  etc.,  and  a  knowledge  of  best  practice 
on  the  part  of  the  designer. 


Figs.  96  and  97. — Side  and  end  view  of  rope  brake.  This  type  of  brake  is  easily  constructed  of 
material  at  hand  and  being  self-adjusting  needs  no  accurate  fatting.^  For  large  powers  the 
number  of  ropes  may  be  increased.  It  is  considered  a  most  convenient  and  reliable  brake. 
In  the  figure  the  spring  balance,  B,  is  shown  in  a  horizontal  position.  This  is  not  necessary; 
if  convenient  the  vertical  position  may  be  used.  The  ropes  are  held  to  the  pulley  or  fly_ wheel 
face  by  blocks  of  wood,  O.  The  weight  at  W,  may  be  replaced  by  a  spring  balance  if  desirable. 
To  calculate  the  brake  horse  power,  subtract  the  pull  registered  by  the  spring  balance,  B, 
from  the  weight  W.  The  lever  arm  is  the  radius  of  the  pulley  plus  one-half  the  diameter  of  the 
rope.    The  formula  is, 

*B.  H.  P.  =27rR  N  (W  — B) 
33,000 
=  .0001904  RxN  (W  — B) 

In  the  formula  R  =radius  from  center  of  shaft  to  center  of  rope;    N  =revoluiions  per 
minute;    W=weight;    B  =spring  balance. 


For  a  given  piston  speed  evidently  a  short  stroke  engine  will 
make  a  larger  number  of  revolutions  per  minute  than  one  with 

*NOTE. — If  B  be  greater  than  W,  the  engine  is  running  in  the  opposite  direction;  in  this 
case  use  the  formula  B.  H.  P.  =  .0001904  R  N   (B  —  W). 


96 


THE  STEAM  ENGINE 


a  long  stroke.  Thus,  for 
say,  800  ft.  of  piston 
speed,  an  engine  with  1 
ft.  stroke  will  make  800 
-^  (2  XI)  =  400  r.p.m., 
whereas,  for  2  ft.  stroke 
only  800 -^  (2X2)  =  200 
r.p.m.   will   be  required. 

Oues.  What  is  the 
meaning  of  the  term 
high  speed  engine? 

Ans.  It  means  that 
the  number  of  revolu- 
tions per  minute  or 
rotary  speed  is  high,  for 
the  particular  type  of 
engine  in  question.  This 
term  should  not  be  con- 
fused with  high  piston 
speed,  as  it  does  not  re- 
late to  the  piston  speed. 

Fig.  98. — Troy  high  speed  vertical 
automatic  center  crank  engine 
with  self-oiling  system.  Made  in 
sizes  ranging  from  3^^  X4  to 
12X12;  revolutions:  highest  600 
to  350,  standard  400  to  300;  low- 
est, 400  to  275.  The  oiling  system 
consists  of  a  reservoir  in  base  for 
oil,  a  pump  driven  from  the  eccen- 
tric rod,  and  pipe  connections  to 
all  the  bearings.  In  operation 
the  oil  is  drawn  from  the  supply  in  the  engine  base,  through  a  strainer  funnel  and  suction 
pipe  to  the  pump  and  check  valve,  then  driven  through  the  sight  feed,  where  its  movement 
can  be  noted,  to  the  distributing  head  and  thence  through  the  supply  pipes  to  the  bearings, 
keeping  them  flooded;  and,  overflowing,  finds  it  way  back  to  the  reservoir  for  repeated  use. 
Any  water  of  condensation  entering  the  reservoir  is  automatically  carried  away,  leaving  the 
oil.  No  water  can  enter  the  suction  pipe  if  the  designated  amount  of  oil  be  placed  in  the 
engine.  A  special  packing  is  used  in  the  piston  rod  stuffing  box  and  practically  eliminates 
the  passage  of  water. 


THE  STEAM  ENGINE  97 


The  first  step  in  calculating  the  cylinder  dimension  is  to 
arrange  the  horse  power  formula  in  the  proper  form  for  obtaining 
the  value  of  the  unknown  quantity. 

Thus,  starting  with  the  formula 

H.  P.  =  .000004  D'L  N  P .    (1) 

the  quantities  to  be  found  are  D,  the  diameter  of  cylinder  or 
piston,  and  L,  the  length  of  stroke.  Accordingly,  solving  for 
these  quantities 


^2     H.  P.       ^   I  H.  P.         ' 

D   = ^  or  D  =  \ .  .  (2) 

.000004  L  N  P       '  .000004  L  N  P 


L= ^ (3) 

.000004  D'  N  P 


For  those  who  do  not  understand  the  solution  of  equations, 
(2)  and  (3)  are  easily  obtained  from  (1)  as  follows: 

Rule. — On  one  side  the  equality  sign  write  down  the  unknown 
quantity;  on  the  other  side,  1,  the  horse  power  as  numerator,  and  2, 
the  remaining  J  actors  as  denominator. 

Of  course,  when  D  is  the  unknown,  since  it  is  squared  in  the  formula,  the 
square  root  must  be  taken  as  in  (2). 

Example. — Find  the  size  of  cylinder  of  a  Corliss  engine 
to  develop  85  horse  power  when  running  under  the  following 
conditions:  Initial  pressure,  80  lbs.;  J4  cut  off;  mean  back 
pressure,  2  lbs.  (non-condensing)  diagram  factor  .9;  piston  speed 
600  ft.  per  minute. 

The  solution  consists  of  three  steps,  viz.:  finding,  1,  the  mean 
effective  pressure;  2,  the  stroke,  and  3,  the  diameter  of  cylinder. 


98  THE  STEAM  ENGINE 

CASE  1.     DIAGRAM   FACTOR   GIVEN 
1.     Mean  effective  pressure. 

1.  Find  total  number  of  expansions  (neglecting  clear ance).t 
Rule. — One  divided  by  the  reciprocal*  of  the  cut  off. 

1-^1  =  1X4=4 

>i 

2.     Find  mean  forward  pressure. 

Rule. — Multiply   initial   pressure   by    l-\-hyp.    log.    of  expansions,    and 
divide  by  number  of  expansions. 

From  table  page  71,  hyp.  log.  of  4  =  1.3863. 

1+hyp.  log.  4  =  1+1.3863=2.3863 

initial  pressure  absolute  =  80  +  14.7  =94.7 

r           -,                .   94.7X2.3863     kck  :^  ^u 
mean  forward  pressure  = =56.5  lbs.  per  sq.  m. 


3.     Find  mean  effective  pressure. 

Rule. — Subtract  mean  back  pressure  absolute  from  mean  forward  pressure, 
and  multiply  the  difference  by  the  diagram  factor. 

2  lbs.  mean  back  (gauge)  pressure  =  2 +  14.7  =  16.7  lbs.  absolute 

(56.5  —  16.7)  X.9  =35.8  lbs.  per  sq.  in. 

2.     Choice  of  Stroke. 

The  length  of  stroke  must  be  such  as  will  give  a  desirable  number  of 
revolutions,  and  bear  a  proper  relation  to  the  cylinder  diameter.  The 
Corliss  engine  is  a  slow  speed  or  long  stroke  type,  usual  ratio  of  stroke  to 
diameter  being  about  2  :  1  or  more,  hence  of  the  several  lengths  of  stroke 
that  could  be  used,  one  should  be  selected  that  will  come  within  the  ratio 
limits  and  also  give  the  proper  speed  in  developing  the  rated  power. 
Ordinarily  the  revolutions  may  be  from  100  to  125,  and  with  valve  gears 


fNOTE. — It  should  be  understood  that  in  the  example  the  expression  one-quarter  cut  off 
relates  to  the  point  of  stroke  at  which  steam  is  cut  off  by  the  valve  gear;  it  does  not  represent 
the  real  cut  off,  with  respect  to  the  expansion  of  steam,  because  clearance  must  be  considered, 
and  on  this  account  is,  strictly  speaking,  called  the  apparent  cut  off,  which  will  be  explained 
in  the  chapter  on  valve  gears.  The  econornical  range  of  horse  power  being  considerable,  cor- 
rection for  the  apparent  cut  off  need  not  ordinarily  be  made. 

*NOTE. — The  reciprocal  of  the  cut  off  means  one  divided  by  the  cut  off. 


THE  STEAM  ENGINE 


99    ^ 


especially  designed  for  high  speed, 
150  r.  p.  m.,  or  higher.  The  revo- 
lutions or 

R.  P.  M.  =  piston  speed H-2 
X  stroke  (in  feet) 

thus,  for  say,  24"  stroke  and  given 
piston  speed  of  600  feet 

R.  P.  M.=600-^2X^  =  150 

Similarly,  the  following  table 
is  obtained: 

R.  P.  M.  for  600  ft.  piston  speed 


Stroke 

24 

30 

36 

R.  P.  M. 

150 

120 

100 

3.  Diameter  of  cylinder. 

The  m.  e.  p.  obtained  in  1,  is 
35.^  lbs.  per  sq.  ins.;  now  in- 
specting the  table  in  2,  a  trial 
may  be  made  with  the  36"  stroke 
which  gives  100  r.  p.  m.  Sub- 
stituting the  values  in  formula 
(2)  page  97, 


o=v: 


85 


Q00004X  36X100X35. 8 
=  12.8 (a) 


For  the  given  power,  this  di- 
ameter of  cylinder  may  be  used 
with  any  stroke  in  the  table  in 
2  at  the  revolutions  given,  that  is 
the  cylinder  dimension  may  be 

12.8X36  for  100  r.  p.m. 
12.8X30  for  120  r.  p.m. 
12.8  X  24  for  150  r.  p.m. 


100  THE  STEAM  ENGINE 


calling  the  diameter  13  ins.,  in  each  case,  the  stroke  diameter  ratios  are 
2.77,  2.3,  and  1.87  respectively,  the  first  two  being  within  limits  and  the 
■  last  two  small. 

In  the  case  of  a  growing  plant  where  more  power  will  be  soon  required 
the  13  X36  would  be  desirable,  as  the  r.  p.  m.  could  be  increased  considerably 
to  increase  the  power.  Ordinarily,  the  13X30  would  be  desirable,  as  it 
would  cost  less,  and  would  run  at  a  more  desirable  r.  p.  m. 


CASE  2.     DIAGRAM   FACTOR   NOT   GIVEN 

A  graphical  solution  of  the  example  just  given  consists  in 
drawing  the  theoretical  card  corresponding  to  the  given  values 
of  initial  pressure,  cut  off,  etc.,  and  inscribing  in  this  diagram 
a  card  drawn  to  represent  the  "expected"  performance  of  the 
actual  engine.  This  card  is  drawn  after  considering  a  large 
number  of  actual  cards  of  similar  engines  operating  under  similar 
conditions.  Accordingly,  the  more  experienced  the  designer, 
the  nearer  can  he  come  to  drawing  a  card  that  will  represent 
the  actual  performance  of  the  engine. 

The  steps  in  this  graphical  method  are:  1,  drawing  the  theo- 
retical card;  2,  drawinjg  the  expected  card;  3,  finding  the  ex- 
pected m.  e.  p. ;  4,  finding  the  cylinder  dimensions. 

1.  The  theoretical  card. 

In  fig.  100,  draw  the  vacuum  line,  or  line  of  no  pressure  OV.  Using  a 
scale  of  1"=40  lbs.,  draw  the  atmospheric  line  E  D,  a  distance  above 
corresponding  to  14.7  lbs.  and  parallel  to  O  V.  At  a  height  corresponding 
to  94.7  lbs.  abs.  draw  the  admission  line  A  B,  in  length  =  ^  of  E  D;  extend 
A  B,  by  dotted  line  to  3  and  at  points  1,  2,  3,  drop  perpendiculars.  From  O, 
draw  radial  lines  01,  02,  03,  cutting  the  perpendicular  from  B,  at  1',  2',  3' 
respectively;  the  intersection  of  horizontal  lines  from  these  points  with 
the  perpendiculars,  give  points  1",  2",  C,  on  the  expansion  curve,  thus 
completing  the  theoretical  card  A  B  C  D  E,  corresponding  to  the  given  data. 

2.  The  expected  card. 

At  this  point  all  depends  on  the  experience  and  judgment  of  the  designer 
who  sketches  within  the  theoretical  card,  fig.  100,  a  card  which  he  thinks 
will  represent  the  actual  performance  of  the  engine.  He  proceeds  about 
as  follows:    The  initial  pressure  being  given  instead   of  boiler  pressure, 


THE  STEAM  ENGINE 


101 


no  allowance  is  made  for  drop  between  boiler  and  engine,  hence  the 
expected  admission  line  begins  from  A,  and  proceeds  toward  B,  first  hori- 
zontally, and  then  begins  to  slope  downward  (though  very  slightly)  because 
of  pressure  drop  due  to  initial  condensation  due  to  the  low  temperature  of 
the  cylinder  walls;  approaching  cut  off  at  6,  the  admission  becomes  curved 
because  of  drop  due  co  "wire  drawing",  as  the  valve  closes.* 

The  expected  expfansion  line  then  begins  at  6,  at  a  lower  pressure  than  B. 
Because  of  this  condition  and  the  fact  that  condensation  continues,  part 
of  the  stroke,  say  to  c,  a  point  at  which  the  temperature  of  the  steam  and 
cylinder  walls  are  considered  the  same. 


94.7 
90 


Fig.  100. — The  expected  diagram.  Having  drawn  the  theoretical  card  A  B  C  D  E,  success  in 
obtaining  the  proper  diagram  factor  depends  upon  the  experience  and  judgment  of  the 
designer  which  guides  him  in  sketching  in  the  expected  diagram  a  b  c  d  e  f  g,  which  he 
"expects"  will  represent  the  actual  performance  of  the  engine  when  built  and  operating 
under  the  specified  conditions. 

Expansion  beyond  c,  will  evidently  take  place  at  temperature  lower 
than  that  of  the  cylinder  walls,  which  is  regarded  as  practically  constant. 
Accordingly  re-evaporation  of  some  of  the  steam  previously  condensed 
will  take  place  causing  the  expected  curve  to  approach  and  rise  above  the 
theoretical  curve  between  c  and  d. 

At  d,  pre-release  occurs,  the  gradual  opening  of  the  exhaust  valve  causes 
a  pressure  drop,  represented  by  the  rounded  end  or  toe  d  e.  Release  is 
taken  at  2  lbs.,  and  represented  by  a  Hne  extending  from  e,  to  some  point 


NOTE. — In  the  Corliss  engine  this  loss  is  reduced  to  a  minimum  owing  to  the  very  quick 
movement  of  the  valve,  but  the  act  of  cutting  off  steam  in  any  valve  gear  is  far  from  being 
instantaneous. 


102  THE  STEAM  ENGINE 


/,  selected  by  the  designer  at  which  the  exhaust  valve  closes,  that  is,  at 
which  compression  begins. 

The  compression  curve  extending  from/,  to  g,  may  be  sketched  in  by  eye, 
or  if  greater  accuracy  be  desired,  by  constructing  a  hyperbolic  curve, 
based  on  the  clearance.  The  latter  in  the  Corliss  engine  may  be  taken  at 
21/2  to  3%  of  the  piston  displacement. 

3.  The  expected  M.  E.  P. 

This  is  determined  from  the  area  of  che  expected  card,  fig.  100,  by  means 
of  the  following  formula: 

expected  m.  e.  p.  =   ^^^^  ^^  ^^^^   Xpressure  scale (1) 

length  of  card 

The  area  is  best  obtained  by  use  of  a  planimeter,  or  approximately  by 
ordinates  (explained  in  figure  81).  In  this  case  the  area  is  by  planimeter; 
length  of  card  4  ins.,  and  pressure  scale  40..    Substituting  these  values  in  (1)  - 

expected  m.  e.  p.  =^i^-^X40=34.2  lbs.  per  sq.  ins. 
4 

4.  Cylinder  dimensions. 

In  Case  I,  a  36''  stroke  was  selected  for  future  excess  power  demands, 
and  a  30"  stroke  where  such  provision  was  not  made.  Substituting  the  value 
34.2  lbs.  per  sq.  ins.  expected  m.  e.  p.  in  the  formula  for  the  36  ins.  stroke 


.=V 


85 

000004X36X100X34.2"-^^'-^  ^^^-  ^^^  ^^  ^^^• 


As  in  Case  I,  the  cylinder  dimensions  could  be  either  13X36,  or  13X30 
according  to  conditions  and  judgment  of  the  designer. 


STEAM  ENGINE  PARTS  103 


CHAPTER  3 
STEAM  ENGINE  PARTS 


The  numerous  parts  of  which  an  engine  is  composed  may  be 
divided  into  three  classes  with  respect  to  operation,  as 

1.  Stationary; 

2.  Revolving; 

3.  Reciprocating. 

The  stationary  parts  are  the  cyhnder,  frame  and  bed  plate;  the  revolving 
parts,  the  shaft,  eccentric;  the  reciprocating  parts,  the  piston,  piston  rod, 
crosshead,  connecting  rod,  valve,  and  valve  gear.  Of  these  various  parts 
■  the  greatest  proportion  are  reciprocating,  and  these,  especially  in  the  case 
of  high  speed  engines,  must  be  of*  minimum  weight  consistent  with  proper 
strength  to  avoid  undue  vibration,  thus,  the  skill  of  the  designer  is  shown 
by  his  treatment  of  these  parts. 

The  Cylinder. — This  consists  of  a  cylindrical  chamber, 
as  shown  in  figs.  101,  and  102,  bored  true,  and  in  which  is 
fitted  a  steam  tight  piston,  free  to  move  from  one  end  to  the 
other. 

The  distance  in  which  the  piston,  during  its  stroke,  is  in 
contact  with  the  cylinder  is  called  the  bore.  To  prevent  a 
"shoulder"  being  formed  at  either  end  by  the  action  of  the  piston, 
the  diameter  at  these  points  is  enlarged  so  that  the 'piston 
slightly  over  travels  the  bore.  The  enlarged  sections  are  known 
as  the  counter-bore. 

The  cylinder  is  closed  by  two  covers  called  cylinder  heads.  These  are 
secured  to  the  flanged  ends  or  jaces  by  bolts.  All  bearing  surfaces  are 
finished  smooth  and  true  and  a  steam  tight  joint  is  made  at  each  face  by 


104 


STEAM  ENGINE  PARTS 


STEAM  ENGINE  PARTS 


105 


I 


106  STEAM  ENGINE  PARTS 


inserting  a  gasket,  that  is,  a  thin  sheet  of  packing  cut  to  size,  and  then  bolting 
the  parts  firmly  together. 

The  distance  between  the  faces  of  the  cylinder  is  such  that  the  piston 
does  not  touch  either  head  when  at  the  end  of  the  stroke.  A  small  space 
is  always  left  between  to  prevent  contact.  This  volume  plus  the  volume 
of  the  steam  passage  betv/een  the  cylinder  and  the  valve  seat  is  called  the 
clearance,  and  is  expressed  as  a  percentage  of  the  volume  displaced  by  the 
piston  in  one  stroke. 

The  term  clearance  is  also  used  to  denote  the  distance  between  the 
cylinder  head  and  the  piston  when  the  latter  is  at  either  end  of  the  stroke, 
being  called  the  linear  clearance. 

A  hole  is  bored  through  one  head  for  the  piston  rod,  a  steam  tight  joint 
being  made  by  means  of  a  stuffing  box.  This  consists  of  a  cylindrical 
chamber,  of  somewhat  larger  diameter  than  the  rod.  The  annular  space  thus 
left  around  the  rod  is  filled  with  fibrous,  or  metallic  packing  which  is  com- 
pressed so  as  to  form  a  tight  joint  by  a  hollow  sleeve  called  a  gland.  The 
latter  is  forced  into  the  stuffing  box  to  bring  the  necessary  pressure  on  the 
packing  by  adjusting  the  two  bolts.  In  some  cases  a  screw  stuffing  box  is 
provided,  similar  to  the  one  shown  for  the  valve  stem;  this  is  a  lighter 
construction  but  is  liable  to  come  unscrewed  unless  locked. 

The  cylinder  has  a  projection  on  one  side  called  the  steam  chest  in  which 
is  the  valve.  The  steam  chest  is  closed  by  a  plate  known  as  the  valve  or  steam 
chest  cover;  this  is  fastened  to  the  steam  chest  by  bolts,  a  gasket  being 
placed  between  the  bearing  surfaces  to  make  a  tight  joint. 

In  operation,  steam  passes  from  the  steam  chest  to  the  cylinder  ends 
through  the  steam  passages,  between  which  is  the  exhaust  passage. 

At  the  beginning  of  these  passages  is  a  smooth  flat  surface  on  which  the 
valve  moves  and  which  is  called  the  valve  seat. 

The  two  openings  in  the  valve  seat  to  steam  passages  are  called  the  steam 
ports,  and  the  opening  to  exhaust  passage  the  exhaust  port.  Careful  dis- 
tinction should  be  made  between  the  terms  passages  and  ports. 

The  valve  as  shown  overtravels  the  length  of  the  seat  to  prevent  the 
formation  of  a  shoulder  by  wear,  and  also,  in  the  case  of  unbalanced  valves 
to  reduce  the  load  on  the  valve  pressing  it  against  its  seat  due  to  the  steam 
pressure,  as  when  the  steam  edge  of  the  valve  overtravels  the  seat  limit,  the 
pressure  on  that  portion  of  the  valve  not  in  contact  with  the  seat  is  neutral- 
ized. Motion  is  transmitted  to  the  valve  by  the  valve  stem.  A  stuffing  box 
is  provided  to  make  a  steam  tight  joint  at  the  point  where  the  valve  stem 
passes  out  of  the  steam  chest. 

Loss  of  heat  by  radiation  is  partially  prevented  by  covering  the  cylinder 
with  asbestos  or  other  insulating  material.  For  external  appearance  and 
to  protect  the  insulating  material,  it  is  covered  with  a  wooden  or  metallic 
lagging. 

An  interior  view  of  a  steam  chest  is  shown  in  fig.  102.  The  valve  being 
removed,  the  valve  seat  is  exposed  showing  the  steam  and  exhaust  ports. 


At  the  side  of  the  cyHnder  is  a  projecting  flanged  pipe  which  forms  the 
outlet  from  the  exhaust  passage. 

The  depression  at  the  farther  end  should  be  noted;  this  terminates  the 
valve  seat  and  allows  the  valve  to  overtravel  for  reasons  already  explained. 

There  is  a  slight  projection  on  the  two  side  walls  of  the  steam  chest  which 
is  planed  smooth  to  serve  as  a  guide  for  the  valve  in  its  direction  of  travel. 
It  also  permits  the  valve  being  made  narrower  than  the  steam  chest  so  that 
it  may  be  easily  inserted.    These  projections  are  sometimes  omitted. 


Fig.  103. — Harris-Corliss  cylinder  with  steam  jacket.  The  section  in  black  is  the  liner  or 
working  barrel,  around  which  live  steam  circulates.  The  object  of  a  jacket  is  to  reduce 
condensation  withm  the  barrel  or  cylinder  proper. 

Jacketed  Cylinders. — Sometimes  a  liner  or  working  barrel 
of  somewhat  smaller  diameter  is  fitted  to  a  cylinder  as  shown 
in  fig.  103,  leaving  an  annular  space  all  around  through  which 
live  steam  circulates.  The  object  of  this  is  to  supply  heat  to  the 
walls  of  the  barrel,  to  make  up  for  that  abstracted  during  expansion 
and  exhaust,  so  that  at  admission,  the  walls  will  be  as  hot  as 
possible,  thus  preventing  condensation  or  reducing  it  to  a 
minimum. 


108  STEAM  ENGINE  PARTS 

In  general,  the  greater  the  number  of  expansion,  the  greater  the 
reduction  of  feed  water  consumption  due  to  the  use  of  a  jacket."^ 

Prof.  Schrooter  from  his  work  on  the  triple  expansion  engines  at  Augs- 
burg, and  from  the  results  of  his  tests  of  the  jacket  efficiency  on  a  small 
engine  of  the  Sulzer  type  in  his  own  laboratory  concludes  as  follows: 
1.  The  value  of  the  jacket  may  vary  within  very  wide  limits,  or  even 
become  negative;  2,  the  shorter  the  cut  off,  the  greater  the  gain  by  the  use 
of  a  jacket;  3,  the  use  of  higher  pressure  in  the  jacket  than  in  the  cylinder 
produces  an  advantage ;  4,  the  high  pressure  cylinder  may  be  left  un jacketed 
without  great  loss,  but  the  other  should  always  be  jacketed. 

■  The  usual  method  of  fitting  liners  or  working  barrels  to  cylinders  to  form 
steam  jackets  are  shown  in  figs.  104  to  106.  The  construction  is  such  that 
the  liner  is  free  to  expand  or  contract  independently  of  the  cylinder  casting, 
a  steam  tight  joint  being  made  between  the  two  by  means  of  an  ordinary 
stuffing  box  packed  with  fibrous  packing. 

For  equal  conditions,  the  gain  by  jacketing  is  greater  for  small  cylinders 
than  for  large,  because  in  small  cylinders  the  cylinder  surface  per  unit 


*NOTE. — ^A  test  of  the  Laketon  triple  expansion  pumping  engine  showed  a  gain  of 
8.3  per  cent  by  the  use  of  the  jackets,  but  Prof.  Denton  points  out  that  all  but  1.9  per  cent  of  the 
gain  was  ascribable  to  the  greater  range  of  expansion  used  with  the  jackets  (Trans.  A.  S.  M.  E., 
XIV,  1412). 

NOTE. — The  value  of  the  steam  jacket  may  be  judged  from  the  experiments  of  Bryan 
Donkin  made  at  Bermondsly  on  a  single  vertical  experimental  engine.  The  details  of  the 
engine  are:  Size  6X8;  Meyer  valve  gear;  barrel  and  heads  jacketed,  also  valve  chest  cover, 
steam  is  supplied  to  each  of  the  four  jackets  direct  from  the  boiler  by  a  separate  pipe.  By 
special  arrangement  the  water  from  the  cylinder  body  jacket  was  divided  into  two  portions 
and  the  weight  of  them  given  separately.  The  first  portion  consisted  of  the  steam  condensed 
on  the  inner  vertical  surface  of  the  jacket  due  to  the  heat  passing  through  the  walls  into  the 
cylinder;  the  other  portion  that  condensed  on  the  outer  vertical  surface  of  the  jacket  due  to 
heat  uselessly  radiated  outwards  owing  to_ imperfect  external  covering.  Observations  were 
taken  with  small  thermometers  inserted  in  one-eighth  inch  holes,  drilled  into  the  metal 
walls  and  filled  with  mercury.  In  all  experiments  the  feed  water  always  included  the  whole 
of  the  jacket  water. 

Mr.  Donkin  found  that  with  about  50  lbs.  boiler  pressure,  running  condensing,  the 
saving  due  to  the  jacket  was:  40.4%  at  6.8  expansions;  40.1%  at  6  expan.;  38.5%  at  4.8 
expan.;  31.1%  at  3.7  expan.;  23.1%  at  1.8  expansions.  In  Mr.  Donkin's  experiments,  the 
temperature  of  the  cylinder  itself  was  observed  at  various  points  between  the  inner  and  outer 
surface  by  means  of  thermometer  inserted  in  small  holes  drilled  in  the  metal.  When  the 
jackets  were  in  use  the  mean  temperature  of  the  metal  was  almost  equal  to  that  of  the 
steam  on  admission;  when  the  jackets  were  not  in  use  it  was  some  50°  lower.  The  temperature 
as  shown  by  the  thermometer  was  nearly  uniform  from  inside  to  outside;  for  the  periodic 
chilling  of  the  innermost  layer  of  metal  by  re- evaporation  of  condensed  steam  was  too  super- 
ficial to  be  at  all  fully  exhibited  in  this  way.  From  the  experiments  it  may  be  inferred  that  the 
smaller  the  cylinder,  the  greater  is  the  percentage  of  gain  from  the  use  of  a  steam  jacket 
arising  doubtless  from  the  fact  that  a  small  cylinder  gives  a  larger  jacket  surface  for  a  given 
weight  of  steam  passing  through  it,  than  a  larger  cylinder  does.  i2nd  report  of  research 
committee  on  the  value  of  the  steam  jacket.) 

Other  engines  experimented  upon  were:  Compound  jet  condensing  beam  pumping 
engine;  triple  expansion  pumping  engine;  compound  mill  engine.  For  full  particulars  of 
Donkin's  experiments  see  Pro,  Inst.  Mech.  Eng.  1892,  page  464. 


STEAM  ENGINE  PARTS 


109 


weight  of  steam  passing  through  the  engine  is  greater  than  in  large  cylinders. 
In  some  cases  the  jacket  is  so  constructed  that  steam  supply  for  the  engine 
is  used  for  the  jacket,  passing  through  the  jacket  on  its  way  to  the  engine. 

Stuffing   Boxes. — By  definition,   a  stuffing  box  is  a  device 
affording  passage  and  lengthwise  or  rotary  motion  of  a  piece,  as 


FLANGF. 


W^\^ 


Figs.  104  to  106. — ^Various  methods  of  fitting  liners  to  cylinders.  Fig.  104  is  a  form  of  liner 
having  a  flange  at  the  bottom  end  secured  to  the  cylinder  by  sunk  head  bolts.  At  the  other  end 
a  steam  tight  joint  is  secured  by  a  stuffing  box  with  packing  ring.  Fig.  105  shows  a  liner  with 
recessed  joint  at  one  end  and  at  the  other  a  plain  contact  joint  reinforced  by  caulking  a  soft 
copper  ring  into  a  dovetailed  groove.  The  figure  shows  a  method  of  draining  condensate 
from  the  top  head  by  the  pipe  siphon.  Fig.  106  shows  a  method  of  bolting  the  liner  fast 
at  the  top  with  bolts  spaced  as  far  around  the  cylinder  as  the  ports  will  admit.  Although  this 
method  has  been  employed  on  U.  S.  Cruisers,  the  author  does  not  consider  it  good  practice. 
In  fitting,  the  liner  is  forced  into  place  but  because  of  the  danger  of  bringing  too  much  strain 
upon  the  cyhnder,  the  fit  cannot  be  made  tight  enough  to  eliminate  leakage,  hence  the 
necessity  for  stuffing  boxes.  The  flanged  joints  at  the  bottom  may  be  made  tight  with  a 
gasket  but  usually  a  heavy  coat  of  red  lead  or  mastic  cement  is  sufficient. 

of  a  piston  rod  or  shaft,  while  maintaining  a  fluid  tight  joint  about 
the  moving  part. 

In  construction,  there  is  an  annular  space  around  the  moving  part, 
closed  by  an  adjustable  flanged  bushing  or  gland  so  that  when  the  annular 


110 


STEAM  ENGINE  PARTS 


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CROSSHCAD  END 

Fig.  107. — Duplex  block  metallic  packing  (U.  S.  Metallic  Packing  Co.),  for  stationary  and 
marine  engine  piston  rods  and  valve  stems.  This  packing  is  in  two  independent  sections, 
separated  by  the  dividing  piece  10,  the  upper  section  consisting  of  white  metal  rings  13,  wnth 
vibrating  cup,  follower,  etc.,  being  in  the  stuffing  box,  and  the  lower  section  consisting  of 
blocks  4,  with  horn  rings,  sliding  plate,  ball  joint,  etc.,  being  contained  in  the  gland  1.  The 
upper  or  inner  set  of  packings  consists  of  three  babbitt  metal  rings  13,  each  in  three  parts, 
contained  in  the  vibrating  cup  12.  There  is  a  ground  joint  between  the  flat  face  of  the 
vibrating  cup  12,  and  the  dividing  piece  10.  Above  the  babbitt  metal  rings  13,  come  the  follower 
14,  and  the  upper  spring  bushing  15,  in  pockets  in  which  are  contained  the  upper  follower 
springs  16,  and  then  in  the  bottom  of  the  stuffing  box  the  preventer  17,  varying  in  length 
according  to  the  depth  of  the  box.  As  the  dividing  piece  10,  is  bolted  to  the  face  of  the  stuf- 
fing box  independently  of  the  gland  1,  which  contains  the  lower  or  outer  set  of  packing, 
the  blocks  in  the  lower  set  may  be  renewed  or  any  other  necessary  work  done  to  same  with- 

f  out  taking  down  the  upper  set  of  packing  or  in  any  way  disturbing  it.  The  lower  or  outer 
section  of  the  packing  consists  of  eight  blocks  4,  babbitt  lined,  which  are  held  in  rings  5, 
having  horns  holding  springs  6.  The  packing  blocks  are  put  together  in  sections  four  blocks 
to  a  section.    Each  section  is  composed  of  two  working  blocks  and  two  guide  blocks.     The 

k  joints  between  the  blocks  in  each  section  are  at  right  angles  to  each  other,  thus  "breaking 
joint."  Small  follower  springs  9,  in  pockets  are  also  used'behind  the  follower  plate  7.  The 
combination  of  the  sliding  plates  and  ball  ring  2,  having  ground  surfaces,  allows  for  the  move- 
ment of  rods  out  of  line.    The  spring  pressure  is  so  regulated  as  to  merely  hold  the  parts  in 

•  place  when  the  engine  is  running  without  steam.  A  hole  is  drilled  in  the  gland  at  A  for  a 
nipple  and  .globe  valve  so  that  condensation  can  be  drained  off.  The  parts  are:  1,  gland; 
2,  ball  ring;  3,  sliding  plate;  4,  blocks;  5,  horn  rings;  6,  horn  ring  springs;  7,  follower 
plate:    8,  spring  bushing;    9,  follower  springs;    10,  dividing  piece;    11,  swab-holder  plate; 

'  12,  vibrating  cup;  13,  babbitt  rings;  14,  follower;  15,  upper  spring  bushing;  16,  upper 
follower  springs;     17,  preventer. 


STEAM  E^^GINE  PARTS 


111 


space  is  filled  with  fibrous  packing  the  proper  pressure  may  be  applied  to 
same  to  secure  a  tight  joint. 


Figs.  108  and  109. — Stuffing  box  which  forms  a  steam  tight  joint  for  the  piston  or  valve  stem. 
By  means  of  the  adjustable  sleeve,  the  proper  pressure  Is  brought  to  bear  on  the  packing 
to  prevent  leakage  of  the  steam. 


Figs.  110  to  115. — Various  types  of  stuffing  box  Fig  1 10  shows  a  piain  box  with  ■jtud  adjust- 
ment; fig.  113,  plam  box  with  screw  adjustment.  Figs.  Ill  and  114  show  the  long  sleeve  type 
of  box,  these  being  identical  except  that  m  fig.  1 1 4  the  sleeve  ha.^  spaced  grooves,  as  an  extra 
provision  against  leakage  In  construction  the  sleeve  is  an  accurate  sliding  fit  with  the  rod  and 
is  secured  by  the  flange  which  is  Held  in  a  stuffing  box,  the  latter  not  only  serving  to  prevent 
leakage  around  the  outside  of  the  sleeve  but  to  allow  lateral  movement  ot  the  sleeve  to 
accommodate  it  to  any  irregularity  in  the  movement  of  the  rod.  Figs,  1 1 2  and  1 15  show  two 
types  of  metallic  packing  of  the  ring  iorm.  The  rings  have  parallel  faces  and  are  held  be- 
tween the  collars  of  a  cast  iron  casing  and  the  segments  are  pressed  in\ward  upon  the  rod 
by  circumferential  springs.  In  fig.  1 12,  each  ring  is  oivided  radially  into  three  segments,  and 
the  two  rings  in  one  compartment  break  joint,  oeing  kept  in  place  by  little  dowels  which 
projec  .  into  the  gap  in  the  elastic  confining  ring.    The  casing  is  divided  lengthwise  in  halves. 


112  STEAM  ENGINE  PARTS 

In  some  cases  the  end  surfaces  of  the  annular  chamber  containing  the 
packing  are  flat  but  usually  are  slightly  conical  to  force  the  packing  against 
the  rod.  The  accompanying  cuts  show  various  types  of  stuffing  box,  and 
forms  of  packing  used  in  same. 

In  design,  the  length  and  diameter  of  the  stuffiing  box  depends  on  the 
material  used  and  the  working  pressure.  In  the  case  of  horizontal  cylinders 
when  the  stuffing  box  becomes  also  a  bearing,  it  may  be  made  longer. 
For  the  valve  stem,  the  box  is  proportionately  deeper  than  for  the  piston  rod. 

In  general,  the  stuffiing  box  may  be  from  2  to  3  times  the  diameter  of  the 
rod,  and  its  diameter  from  1  ^  to  1^4  times  diameter  of  rod. 

In  some  cases  packing  under  pressure  is  dispensed  with  and  a  long  plain 
sleeve  depended  on  for  a  tight  joint,  the  long  close  sliding  fit  between  the 
rod  and  sleeve  preventing  leakage.  The  plain  sleeve  may  be  modified  with 
several  grooves  spaced  along  its  length  to  arrest  the  motion  of  any  steam 
tending  to  leak  through. 

The  Piston. — A  piston  may  be  described  as  a  device  for 
receiving  the  pressure  of,  or  operating  upon,  a  liquid  or  gas  in  a 
cylinder  or  other  enclosing  vessel, 

Pistofis  may   be   classified: 

1.  With  respect  to  shape,  as 

a.  Cylindrical  {|°J^,^.  " 

h.  Conical; 

c.  Rectangular. 

2.  With  respect  to  motion,   as 

a.  Reciprocating; 
h.  Oscillating; 
c.  Rotating. 

3.  With  respect  to  the  action  of  the  steam  as 

a.  Single  acting ; 
h.  Double  acting. 

The  cylindrical  reciprocating  piston  is  the  most  usual  form  and  consists 
essentially  of  a  disc  attached  to  a  rod  and  having  rings  which  press  against 
the  cylinder  walls  to  secure  a  steam  tight  joint. 

For  high  speed  engines,  especially  those  of  the  marine  type,  where  the 
center  of  gravity  of  the  engine  must  be  a  minimum,  the  piston  is  usually 


STEAM  ENGINE  PARTS 


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shaped  like  a  cone,  as  this  gives 
minimum  weight,  thus  reduc- 
ing vibration;  its  shape  per- 
mits shortening  the  height  of 
the  engine  because  the  stuffing 
box  projects  very  Httle  if  any 
beyond  the  cyHnder  head. 

A  rectangular  reciprocating 
piston  consists  of  a  square 
plate  arranged  to  move  to  and 
fro  in  a  rectangular  box  the 
steam  pressure  being  received 
on  the  ends. 

iVn  oscillating  piston  is 
virtually  the  same  as  a  re- 
ciprocating piston,  but  be- 
cause of  the  lateral  stresses, 
it  is  designed  preferably  with 
a  wider  rim  giving  more  bear- 
ing surface  to  reduce  wear. 


Fig.  125. — Early  junk  packing.  This 
packing  could  neither  be  examined 
nor  renewed  without  removing  the  pis- 
ton from  the  cylinder.  To  Remedy 
this,  the  groove  was  made  v/ithout 
a  flange  at  the  end  farthest  from  the 
crank,  and  a  false  flange  called  a  junk 
ring  was  bolted  to  the  piston  to  retain 
the  junk  in  place  and  admit  of  its 
being  removed  without  taking  out 
the  piston.  The  term  "junk  ring" 
is  still  in  use  although  junk  is  no 
longer  used  to  pack  pistons;  a  better 
term  is  follower  ring. 

Rotary  engines  have  a  rec- 
tangular rotating  pistoix  or 
rectangular  plate  oscillating 
in  a  sector  cylinder  and 
attached  to  a  rack  shaft  or  an 
eccentric  or  toothed  cam. 

The  distinguishing  feature 
of  the  various  type  of  piston 
are  shown  in  the  accompany- 
ing cuts. 


STEAM  ENGINE  PARTS 


115 


The  three  essential  requirements  of  a  piston  are: 

1.  Strength  to  withstand  the  pressure  of  the  steam. 

2.  A   steam  tight   joint   between  its   circumference   and   the 
'  cylinder  walls ; 

3.  Ability  to  move  with  very  little  friction. 

SNAP    RriSfGS 


y///////////////^A 


^///////////////////. 


y/////////////////A 


Fig.  12G. — "Snap"  piston  rings.  First  used  by  Ramsbottom,  an  English  engineer,  and  some- 
times called  "Ramsbottom 's  rings."  They  are  turned  somewhat  larger  in  external  diameter 
than  the  bore  of  the  cylinder,  and  after  being  cut  across  so  that  they  may  be  compressed 
to  fit  the  cylinder  bore,  are  fitted  into  recesses  turned  in  the  piston  face. 


According  to  Seaton,  in  the  early  days,  owing  to  imperfect  tools,  cylinders 
were  not  bored  true  nor  were  the  sides  very  smooth.  Since  the  steam 
pressures  at  that  time  were  quite  low,  pistons  could  be  made  steam  tight 
by  coiling  rope  or  junk  soaked  in  melted  tallow  in  a  groove  on  the  rim  of  the 
piston  as  shown  in  fig.  125. 


SNAP    RINGS 


EXTENDED    FOLLOWER 


Fig.   127. — Snap  rings  fitted  to  extended  follower, 
taking  out  the  piston. 


This  permits  removal  of  rings  without 


The  gradual  increase  in  steam  pressures  soon  caused  the  junk  packing 
to  give  way  to  something  more  substantial. 

Ramsbottom  was  the  first  to  introduce  metallic  rings  for  piston  packing. 
These  rings,  of  small  rectangular  cross  section,  are  turned  somewhat  larger 
in  external  diameter  than  the  cylinder  bore,  and  after  being  cut  across, 


116 


STEAM  ENGINE  PARTS 


enough  metal  is  filed  off  at  the  cut  so  as  to  compress  them  to  fit  the  cylinder 
with  the  proper  tension.  The  piston  is  turned  to  an  easy  fit  and  the  rings 
fitted  into  recesses  turned  in  its  edge. 


BULL    RING 


FOLLOWER     RING 

rr:\  f. 


PACKING   RINGS 


Fig,  128. — Snap  rings  fitted  to  hull  ring.  This  is  a  modified  form  of  the  junk  ring,  the  projecting 
spigot  which  carries  the  snap  rings  is  cast  separate  as  shown.  The  bull  ring  is  held  in  place 
by  a  follower  plate. 


m 


Figs.  129  and  130. — Mode  of  turning  snap  rings  to  secure  uniform  pressure  along  the  circumfer- 
ence.    The  ring  is  cut  at  the  thinnest  section. 


vm  [ 


I 


Figs.  131  to  133. — Different  methods  of  cutting  snap  rings. 


STEAM  ENGINE  PARTS 


\Vi 


These  rings  are  usually  called  snap  rings,  since  in  putting  them  on  the 
piston  they  "snap  together"  when  they  fall  into  the  recesses. 

In  fig.  126  is  shown  a  piston  fitted  with  two  snap  rings ;  when  placed  so  the 
joints  are  not  in  Hne,  the  piston  is  practically  steam  tight.  This  is  a  de- 
sirable arrangement  for  small,  quick  running  engines,  but  for  large  engines 
it  has  the  objection  that  the  rings  cannot  be  removed  without  taking  out 
the  piston.  This  is  overcome  by  fitting  an  extended  follower  consisting  of 
a  ring  having  cast  with  it  a  cylindrical  extension,  which  goes  down  into  a 
recess,  and  which  is  bolted  to  the  outside  face  of  the  piston,  snap  rings  being 
fitted  into  recesses  turned  on  the  outer  circumference  of  the  spigot  as  shown 


FOLLOWER    PLATE 


SPRINGS 


TONGUE    PIECE 


Figs.  134  and  135. — Box  piston.  To  reduce  weight,  large  pistons  are  usually  cast  hollow  with 
radial  ribs.  A  single  packing  ring  is  shown  pressed  against  the  cylinder  bore  by  the  springs  S. 
The  ring  joint  is  closed  by  a  tongue  piece  T. 

in  fig.  127.  By  removing  the  bolts,  the  extended  follower  which  carries  the 
snap  rings  may  be  easily  removed  from  the  cylinder. 

A  modification  of  this  arrangement  consists  of  casting  the  extension 
separate.  It  is  then  called  a  hull  ring  and  as  shown  in  fig.  128  is  held  in  place, 
together  with  the  packing  rings,  by  another  ring  called  the  follower  ring. 

Snap  rings  are  usually  made  of  tough,  close  grained  cast  iron,  and  turned 
eccentric  as  shown  in  fig.  129,  being  cut  at  the  thinnest  part.    The  object  of 


118 


STEAM  ENGINE  PARTS 


PACKING  RIMG         F^^^. 


Figs.  136  to  140.— Murray- 
Corliss  hollow  piston 
without  follower. 


Figs.  141  to  144.-— 

Murray^  Corliss 
built  up  piston. 
The  packing  ring 
i  s  carried  on  a  3  unk 
ring,  and  retained 
in  place  by  a  fol- 
lower and  follower 
plate.  By  un- 
"  screwing  thebolts, 
all  these  parts  are 
easily  taken  out 
without  removing 
the  piston  from 
the  cylinder. 


STEAM  ENGINE  PARTS 


119 


this  is  to  cause  the  ring  to  press  against  the  cylinder  bore  with  uniform 
pressure  at  all  points  on  the  circumference. 

The  several  ways  of  cutting  snap  rings  are  shown  in  figs.  131  to  133.  Re- 
cesses for  snap  rings  are  turned  deeper  than  the  thickness  of  the  rings  to 
allow  a  transverse  movement  independent  of  the  piston  body,  thus  pro- 
viding for  lack  of  alignment  between  the  piston  and  the  cylinder. 

In  large  cylinders,  the  necessary  pressure  of  the  ring  against  the  cylinder  is 
se<;;ured  by  means  of  a  series  of  springs  as  shown  in  figs.  134  and  135.  In  this 
construction  the  packing  ring  usually  consists  of  one  large  ring  pressed 
outwards  against  the  cylinder  by  springs,  and  retained  in  place  by  a  follower 
plate. 


Fig.  145. — Box  piston  with  wrought  iron  stay  bolts  instead  of  radial  ribs,  a  lighter  form  of 
piston  than  that  shown  in  figs.  134  and  135. 


Fig,  146, — Cone  piston  as  used  on  high  speed  marine  engines.    By  making  the  piston  in  the 
form  of  a  cone  great  strength  is  secured,  *thus  reducmg  the  weight. 

For  horizontal  cylinders,  the  bottom  spring  is  removed  and  a  cast  iron 
block  put  in  its  place,  which  takes  the  weight  of  the  piston. 


In  construction,  the  body  of  a  piston  is  either  made: 

1.  SoHd; 

2.  Hollow,  or, 


120 


STEAM  ENGINE  PARTS 


3.  Built  up. 

For  small  engines,  the  solid  type  of  piston  is  used,  being  simply  a  flat 
cast  iron  disc  of  sufficient  thickness  to  receive  the  snap  rings. 


Fig.  147. — Cone  piston  of  forged  steel;   very  light  construction  and  a  desirable  form  for  boats 
of  high  speed. 


.    PACKING 
RINGS 


HUB 

ADJU5TIN6 
"  SCREW 

^FOLLOWER 
^       RING 
OUTER  RING 

BULL  RING 


PACKING  RINGS 


Figs.  148  and  149. — Built  up  piston  consisting  of  spider  and  bull  ring  with  its  packing  rings, 
and  follower  ring. 


STEAM  ENGINE  PARTS 


121 


In  the  larger  sizes,  the  piston  is  made  hollow  with  strengthening  ribs 
for  reinforced  by  stay  bolts  to  reduce  the  weight,  as  shown  in  figs.  134  and  135; 
this  is  called  a  box  piston.  Sometimes,  instead  of  cast  ribs,  this  form  of 
piston  is  reinforced  by  wrought  iron  or  steel  stay  bolts  to  further  reduce 
the  weight,  as  shown  in  fig.  145. 


Figs.  150  to  152. — Brownell  piston,  rings,  and  piston  rod.  The  piston  is  of  the  solid  type, 
cored  and  provided  with  two  spring  packing  rings  cut  in  such  a  manner  that  they  make 
a  steam  tight  joint.  The  piston  is  pressed  on  the  rod  by  hydraulic  pressure,  and  held  in 
place  by  a  nut. 

Where  great  strength  and  light  weight  are  required,  as  in  the  case  of 
high  speed  marine  engines,  pistons  are  made  cone  shaped,  fig.  146,  and  for 
extreme  light  weight  they  are  constructed  of  cast  or  forged  steel,  fig.  147, 
with  one  or  more  packing  ringc; 


Figs.  153  to  156. — Chandler  and  Taylor  piston  nngs,  piston  rod  crosshead  and  wrist  pin. 
The  piston  is  of  the  hollow  cast  iron  type  fitted  with  two  snap  rings.  The  piston  rod  is  made 
of  hammered  crucible  steel.  It  is  fitted  into  the  piston  head  on  a  taper,  and  is  locked  with  a 
heavy  nut.  The  piston  rod  is  screwed  into  the  crosshead.  and  is  locked  in  position  by  a  nut 
jammed  tight  against  the  boss  on  the  crosshead. 

The  built-up  type  of  piston  is  shown  in  figs.  148  and  149.  It  consists  of: 
1,  a  spider  composed  of  several  radial  ribs,  and  a  face  cast  with  a  central  hub, 
and  an  outer  ring;  2,  a  bull  ring  fitting  over  the  outer  ring  and  carrying 
the  packing  rings,  and  3,  a  large  follower  ring  enclosing  the  interior  space 
of  the  piston  and  fastened  to  the  spider  by  a  number  of  bolts.  The  bull 
ring  may  be  adjusted  for  proper  alignment  between  the  piston  and  the 
cylinder  by  means  of  the  set  screws. 


122 


STEAM  ENGINE  PARTS 


The  Piston  Rod. — The  load  due  to  the  steam  pressure  acting 
on  the  piston  is  transmitted  by  the  piston  rod  out  through  the 
stuffing  box  to  the  crosshead  and  connecting  rod.  The  alternate 
stresses  of  compression  and  tension  which  come  upon  the  rod 
in  rapid  succession,  severely  test  the  material  of  which  it  is  made, 
and  since  it  is  desirable  that  the  rod  be  of  small  cross  section, 
it  is  usually  made  of  the  best  steel. 

The  piston  rod  has  a  uniform  cylindrical  shape  except  at  the 
ends  where  it  is  joined  to  piston  and  crosshead.    The  rod  should 


Figs.  157  to  159. — Different  methods  of  fastening  the  piston  rod  to  the  piston.  Fig.  157,  shrink 
fit  with  shoulder,  end  riveted;  fig.  158,.tapered  joint  secured  by  riveting;  fig.  159  tapered  joint 
with  shoulder  to  prevent  seizing,  secured  by  a  nut. 


fit  steam  tight  into  the  piston  and  be  firmly  secured  to  the  latter 
so  as  to  hold  it  rigid  against  shocks. 

There  are  numerous  ways  in  which  the  rod  is  fastened  to  the 
piston. 

A  simple  method  consists  in  reducing  the  diameter  of  the  rod  at  the  end, 
leaving  a  shoulder  and  making  a  shrink  fit  between  the  rod  and  piston; 
the  rod  is  then  riveted  to  the  piston  as  shown  in  fig.  157.  While  this  makes 
a  cheap  and  firm  joint,  it  is  objectionable  in  that  the  rod  cannot  be  readily 
removed. 

To  overcome  this  it  is  usual  to  make  the  end  tapered  or  conical,  as 
shown  in  fig.  158.  If  the  taper  be  very  slight  the  rod  can  be  easily  made  a 
tight  fit,  but  unless  formed  with  a  shoulder  at  the  end  of  the  taper,  it  will 
in  time  become  so  tightly  held  by  the  piston  as  to  withstand  all  attempts  at 
withdrawal,  and  there  would  be  danger  of  splitting  the  piston  by  the 
wedging  action. 


STEAM  ENGINE  PARTS 


123 


In  fig.  159  is  shown  a  rod.  having  a  tapered  end  with  a  shoulder  and  secured 
to  the  piston  by  a  nut.  With  the  proper  taper,  this  rod  may  be  easily 
removed. 

Piston  rods  are  sometimes  fastened  to  large  built  up  pistons  by  means  of 
a  key,  as  shown  in  figs.  160  and  161. 

The  most  usual  method  of  securing  the  rod  to  the  crosshead 
is  a  threaded  joint  and  lock  nut  as  shown  in  fig.  165.  This  has 
the  advantage  of  permitting  adjustment  of  the  rod  length  so  that 


Figs.  160  and  161. — Large  built  up  piston  secufed  to  the  piston  rod  by  means  of  a  key. 


the  clearance  spaces  at  the  cylinder  ends  may  be  equalized  with 
certainty. 

The  manner  in  which  the  rod  is  fitted  to  the  crosshead  de- 
pends somewhat  on  the  type  of  the  latter. 

A  form  commonly  used  for  marine  engines  is  shown  in  figs.  162  to  164, 
consisting  simply  of  a  shoulder,  taper,  and  a  nut  for  holding  the  rod  in 
position. 

Aiother  form  used  extensively  in  marine  and  other  types  of  engines, 
consists  in  forging  the  body  of  the  crosshead  in  one  piece  with  the  rod  as 
shown  in  figs.  166  and  167.     This  construction  has  the  serious  objections, 


124 


STEAM  ENGINE  PARTS 


PISTON 
'  ROD 


-TAPER 


double: 
WRIST  Pin 


TOT'; 


,5TERN  GIB 
AHEAD   GiB 


Figs.  162  to  164. — Marine  type  of  piston  rod  connection  with  crosshead,  having  a  tapered 
joint  secured  by  a  nut.  With  this  construction  the  height  of  the  engine  is  reduced,  lowering 
its  center  of  gravity — a  desirable  feature  for  marine  service. 


Fig.  165. — Usual  method  of  securing  the  piston  rod  to  the  crosshead  by  a  threaded  joint  wi^ii 
lock  nut. 


STEAM  ENGINE  PARTS 


125 


however,  that  if  anything  happen  to  the  rod,  repairs  are  not  so  easily  nor 
quickly  made  as  when  the  rod  is  a  separate  part,  and  the  rod  cannot  be 
removed  without  disconnecting  it  from  the  piston. 

On  locomotives  the  piston  rod  is  usually  secured  to  the  crosshead  by  means 
of  a  key,  figs.  160  and  161,  the  end  of  the  rod  fitting  into  a  tapered  hole 
in  the  crosshead. 

When  the  engines   are  run  intermittently  and   are  *  idle  for 
long  periods,  special  care  should  be  taken  to  protect  the  piston 


FORGED 
ROD  END 


llll  lliliMIIMM^Illl 


Ix 


Figs.  166  and    167. — Piston  rod  and  crosshead  forged  in  one  piece;  an  objectionable  though 
common  construction. 


rod  from  corrosion  and  pitting.     If  a  rod  become  pitted,  it  will» 
be  difficult  to  keep  the  stuffing  box  tight.     "When  an  engine  is 
to  remain  idle  for  a  length  of  time,  the  packing  should  be  removed 
and  the  rod  well  oiled. 

To  prevent  corrosion,  rods  are  sometimes,  made  of  phosphor 
bronze  which  has  about  the  same  strength  as  steel,  and  although 
more  expensive  is  well  worth  the  additional  cost  for  engines  which 
are  to  be  run  only  occasionally. 


126 


STEAM  ENGINE  PARTS 


iTJ    W    jrt    W    ^    0 

"^      U3       ►;>      V*      "^      C 


STEAM  ENGINE  PARTS 


127 


The  Cross  Head  and  Guides.— 

A  cross  head  is  simply  a  ''sliding 
hinge''  which  joins  the  piston  rod  to 
the  connecting  rod.  By  means  of 
guides,  it  prevents  the  bending  of 
the  former  which  otherwise  would 
occur  on  account  of  the  side  thrusts 
of  the  connecting  rod. 

The  design  of  the  cross  head 
varies  more  than  any  other  detail 
of  an  engine. 

It  consists  essentially  of  a  body,  fig. 

230,  having  two  jaws  B  and  C,  between 

which  the  connecting  rod  is  pivoted  by 

the   wrist  pin   W,  fig.  231.      This   pin 

is  inserted  in  holes  bored  in  the  crosshead  body,  and  held  firmly  in  place 

by  a  nut  Z.    At  either  side  of  the  wrist  pin  are  iDcaring  surfaces  M  and  S, 


Fig.  229. — ^A  large  cross  head. 


Figs.  230  and  231.-^Cross  head  and  wrist  pin.  The  wrist  pin  W,  is  inserted  in  boles  bored  through 
the  jaws  B  and  C,  c»nd  the  pin  is  secured  by  the  nut  Z.  M  and  S,  are  the  gibs,  which  bear  on 
the  guides,  and  N,  the  neck  to  which  the  piston  rod  is  fastened. 


128 


STEAM  ENGINE  PARTS 


called  gibs*.  These  run  in  suitable  guides  which  take  the  side  thrusts  of 
the  connecting  rod.  The  two  jaws  come  together  in  a  neck  N  to  which  is 
attached  the  piston  rod. 


Fig.  232. — ^Wrist  pin  with  tapered  ends.    The  pin  is  drawn  into  very  firm  contact  with  the 
cross  head  by  the  nut  on  the  end. 


Fig.  233. — Wrist  pin  with  cylindrical  and  tapered  ends.    A  satisfactory  method  of  attachment 
not  requiring  such  precision  in  machining  as  when  both  ends  are  tapered. 


The  usual  form  of  wrist  pin  is  shown  in  fig.  232.  That  part  in 
contact  with  the  cross  head  body  is  usually  a  tapered  surface 
which  can  be  drawn  into  very  firm  contact  by  the  nut  on  the  end. 


*NOTE, — ^The  cross  head  gibs  are  sometimes  called  shoes  or  slippers. 


STEAM  ENGINE  PARTS 


129 


On  loosening  the  nut,  the  pin  is  easily  withdrawn.     A  key  is 
usually  inserted  in  the  pin  to  prevent  any  turning. 


Fig.  234. — ^Wrist  pin  with  tapered  and  threaded  ends.  This  construction  has  the  objection 
that  the  threads  are  liable  to  injury  on  account  of  the  alternate  transverse  thrust  to  which 
they  are  subjected. 


Fig.  235. — Expanding  wrist  pin.  The  ends  are  split  and  cylindrical,  fitting  accurately  the 
holes  in  the  crosshead  jaws.  An  inner  or  expanding  plug  having  tapered  ends  is  drawn  into 
the  hollow  wrist  pin,  thus  expanding  the  ends,  and  firmly  retaining  the  pin  in  position,  an 
objectionable  construction. 


On  some  crossheads  only  one  end  of  the  wrist  pin  is  tapered  while  the 
other  is  cylindrical  as  shown  in  fig.  233. 

Another  form  of  wrist  pin  is  tapered  at  one  end  and  threaded  at  the 


130 


STEAM  ENGINE  PARTS 


other,  as  shown  in  fig.  234,  a  lock  nut  being  provided  to  retain  the  pin  in 
position. 


Figs.  236  and  237. — ^Approved  method  of  fastening  wrist  pin  where  only  one  side  of  the  cross 
head  is  accessible.  The  pin  which  is  tapered  at  both  ends  is  held  in  place  by  bolts  which 
pass  through  the  flange. 


Pigs.  238  and  239. — Cross  head  with  compression  wrist  pin.  The  cross  head  iaws  A .  B.  are  spht. 
and  may  be  drawn  together  by  the  bolts  M,  S,  which  project  slightly  within  the  holes.  These 
bolts  register  with  notches  N,  N'  cut  in  the  wrist  pin.  When  the  pin  is  m  position  the  jaws 
are  drawn  together  by  bolts,  tightly  gripping  the  pm. 


STEAM  ENGINE  PARTS 


131 


Some  forms  of  wrist  pin  have  no 
taper  at  the  ends.  In  this  class 
belongs  the  expanding  pin  as  shown 
in  fig.  235.  The  wrist  pin  is  bored, 
and  the  bore  tapered  and  split  at 
each  end  where.it  rests  m  the  cross- 
head.  To  the  taper  in  the  pin  is 
fitted  a  steel  plug.  In  attaching  the 
pin  to  the  crosshead,  the  tapered 
plug,  by  means  of  a  finely  threaded 
end  and  nut,  is  drawn  in,  expanding 
the  ends  of  the  wrist  pin  against  the 
sides  of  the  crosshead  This  type  of 
pin  is  used  to  advantage  when  only 
one  side  on  the  crosshead  is  acces- 
sible. However,  the  author's  ex- 
perience with  this  pin  is  that  unless 
it  be  a  very  close  fit  with  the  cross- 
head  it  will  work  loose  after  being 
expanded  by  the  plug,  hence,  it  is 
not  to  be  recommended. 

A  better  method  of  fastening  the 
wrist  pin  where  only  one  side  of  the 
crosshead  is  accessible  is  shown  in 
figs.  236  and  237. 

A  form  of  wrist  pin  known  as  the 
compression  type  is  shown  in  figs.  2  JS 
and  239;  the  ends  of  the  pin  are 
without  taper.  The  pin  which 
accurately  fits  the  holes  in  the  cross- 
head  jaws  is  notched  at  each  end  to 
conform  to  the  bolts  which  project 
within  each  hole.  Each  jaw  is  split 
as  shown,  hence,  w^hen  the  pin  is  in 
position  the  bolts  are  tightened 
which  causes  the  jaws  to  firmly  grip 
the  pin.  Several  notches  are  pro- 
vided at  the  ends  of  the  pin  so  its 
position  may  be  changed  from  time 
to  time  to  prevent  the  pin  becoming 
flattened  on  account  of  wear. 

The  gibs  of  a  crosshead  may 
number  one,  two  or  four,  but 
liberal  bearing  surfaces  are  pro- 
vided on  account  of  the  velocity 
with  which  they  move. 


132 


STEAM  ENGINE  PARTS 


When  a  horizontal  engine  runs  over,  all  the  pressure  and  wear 
comes  upon  the  lower  slipper,  as  in  fig.  240;  if  the  engine  run 
under,  all  the  pressure  and  wear  comes  upon  the  upper  slipper, 
as  in  fisf.  241. 


Fig.  242. — Cross  head  of  the  Reeves  engine.    A  single  bar  machined  on  all  four  sides  serves  as 
the  guides.     This  type  is  frequently  used  on  marine  engines. 

Since  lubricants  flow  over  the  lower  guide  more  easily  than  the  upper, 
and  since  it  is  easier  to  resist  the  strain  on  the  lower  guide,  as  it  usually 
rests  on  the  bed  plate,  it  is  customary  to  cause  horizontal  engines  to  run 
over  rather  than  under. 


Tics.  2-13  and  244. — Twin  City  Corliss  cross  head.  Cylindrical  gibs  with  cross  wedge  adjustment. 


The  greatest  pressure  upon  a  guide  occurs  when  the  piston  is 
near  the  middle  of  its  stroke  which  gradually  diminishes  in  intensity 
to  zero  at  the  end  of  the  stroke. 

The  pressure  on  the  guide  being,  therefore,  very  small  near  the  ends  of  the 


STEAM  ENGINE  PARTS 


133 


stroke  it  is  not  necessary  that  the  entire  surface  of  the  gib  be  in  contact 
■  witb  the  guide  at  these  points.  *  Hence,  the  guides  may  be  shortened  without 
harm  and  the  gib  be  allowed  to  overtravel  to  quite  an  extent  as  shown  in  fig. 
245.  This  is  done  to  advantage  in  engines  of  very  light  weight  or  where  parts 
may  be  made  more  accessible.  In  any  case,  the  gib  should  overtravel  the 
guide  to  prevent  wearing  a  shoulder  at  the  stroke  ends,  f 


The  guides  may  he  one,   two  or  four  in  number.     In  marine 
engines  quite  frequently  only  one  is  used. 


Fig.  245. — -Detail  of  marine  crosshead  and  guides  illustrating  overtravel.  The  gibs  may  pro- 
ject considerably  beyond  the  end  of  the  guide  at  the  stroke  ends,  because  the  thrust  on  the 
guide  diminishes  to  zero  at  the  dead  centers.  The  gibs  should  overtravel  because  a  full 
length  guide  is  unnecessary,  and  the  parts  are  usually  made  more  accessible  by  the  shortened 
guides. 

In  this  case  there  are  two  constructions:  1.  In  which  the  guide  is  sur- 
rounded by  the  crosshead  as  shown  in  fig.  242 ;  2.  In  which  the  crosshead 
projection  containing  the  rubbing  surfaces  is  partially  surrounded  by  the 
guide  as  shov/n  in  figs.  246  and  247. 


*NOTE. — The  side  thrust  on  the  guide  at  any  point  of  the  stroke  is  obtained  from  the 
formula:  side  thrust  =  total  load  on  the  piston  multiplied  by  the  tangent  of  the  angle  which 
the  connecting  rod  makes  with  the  line  of  the  piston  rod  =p  tan0.  When  the  connecting  rod 
is  2^  times  the  length  of  the  stroke  (the  usual  proportion),  the  maximum  angle  of  the  con- 
necting rod  with  the  line  of  piston  is  11°  33'  and  the  tangent  of  this  angle  is  .204  or 
approximately  .2,  hence,  the  greatest  side  thrust  on  the  guide  is  .2  or  20  per  cent,  of  the 
maximum  load  on  the  piston.    For  a  2:1  connecting  rod,  tan 0  =.258;   for  3:1  rod,  tan »  =.169, 

tNOTE. — The  pressure  between  the  crosshead  slipper  and  the  guide  should  not  exceed 
100  pounds  per  square  inch  of  slipper  surface.  On  many  engines  it  is  much  less.  In  loco- 
motives the  pressure  ranges  between  40  and  50  poimds  on  accotmt  of  dirt,  cinders,  etc. 


134 


STEAM  ENGINE  PARTS 


This  type  is  in  fact  two  guides  in  one,  and  is  peculiarly  suited  to  marine 
engines  since  the  area  of  the  backing  guides  B,  B',  need  not  be  as  great  as 
that  of  the  forward  guide  A.  As  a  marine  engine  is  run  in  the  forward 
direction  most  of  the  time  the  backing  guide  may  be  of  small  area  without 
harm,  thus  saving  in  weight  and  making  the  parts  more  accessible. 

Cross  heads  for  marine  engines  are  sometimes  made  without  a 

wrist  pin  and  carry  instead,  the 
wrist  pin  bearing,  the  pin  in  the 
construction  forming  a  part  of  the 
connecting  rod. 


Fig.  248. — Cross  head  of  the  Brown  engine.  It  is  of 
heavy  design,  with  large  wearing  surfaces.  The 
cross  head  pin  is  placed  in  the  center  of  cross  head 
so  that  there  is  no  tendency  towards  a  rocking 
motion.  The  gibs,  which  are  Babbitt  lined,  are 
keyed  up  by  a  wedge  and  screw  from  the  face  of 
crosshead.  This  construction  allows  the  removal 
of  the  gibs  without  taking  the  cross  head  from  the 
guides.  In  adjusting  the  cross  head,  loosen  check 
nut  C,  and  turn  screw  B,  to  the  left  to  drive  wedge 
E,  in  and  force  the  gibs  D,  out  to  the  right  to 
bring  the  gibs  in.  Thrust  collar  A,  is  pinned  to 
adjusting  screw  B. 

Figs.  246  and  247. — Marine  type  of  cross  head 
and  guides.  The  backing  guides  B,  B',  present 
less  area  than  the  forward  guide  A,  a  condition 
well  adapted  to  marine  service  because  the 
allowable  thrust  on  the  guide  is  greater  in  backing  than  when  going  ahead,  since  the  engine 
runs  only  for  short  periods  when  reversed.  More  liberal  surface  should  be  allowed  for  the 
surfaces  B,  B.  in  the  case  of  ferry  boat  engines,  because  tliis  type  of  vessel  runs  equal  periods 
in  both  directions. 


STEAM  ENGINE  PARTS 


135 


A  marine  crosshead  of  this  type  is  shown  in  figs.  166  and  167.  This  is 
formed  on  the  end  of  the  connecting  rod  and  is  objectional  in  some  respects 
as  previously  mentioned. 

Stationary  engines  sometimes  have  crossheads  designed  for 
four  guides,  as  shown  in  figs.  249  and  250,  which  is  a  view  of 
the  Porter-Allen  crosshead  and  wrist  pin. 


CLJJ 


Figs.  249  and  250. — Cross  head  and  wrist  pin  of  the  Porter-Allen  engine.  This  type  which  has 
four  guides  is  used  extensively  on  engines  having  Tangye  frames.  The  wrist  pin  has  tapered 
ends. 


Figs.  251  and  252. — Murray-Corliss  crosshead,  having  cylindrical  gibs  with  wedge  adjustment. 
Besides  the  adjusting  bolts  with  lock  nuts,  two  other  bolts  are  provided  to  prevent  the 
possibility  of  their  becoming  loose. 


136 


STEAM  ENGINE  PARTS 


Locomotive  cross  heads  are  made  for  one,  two  and  four  guides 
as  shown  in  figs.  253,  254,  and  255,  256. 

Y 


Fig.  253. — Locomotive  cross  head  with  single  guide.  On  locomotives  the  piston  rod  is  usually 
attached  to  the  cross  head  by  means  of  a  key  K.  h,  h' ,  are  the  gibs,  and  A,  the  guide  whose 
outer  end  is  bolted  to  a  transverse  piece  or  yoke  Y. 


Figs.  255  and  256. — Locomotive  cross  head  with  four  guides.     The  end  view  at  the  left  shows 
more  clearly  the  location  of  the  guides,  and  the  form  of  the  yoke  which  supports  their  outer 
I     ends. 


STEAM  ENGINE  PARTS 


137 


^P  In  general  the  rubbing  surfaces  of  the  gib  and  guide  may  be 
either  plane,  inclined  or  cylindrical.* 

The  gibs  are  usually  made  of  some  other  metal  because  there  is  less  fric- 
tion between  rubbing  surfaces  of  dissimilar  metals  than  when  made  of 
the  same  metal.  Brass,  white  metal  and  other  alloys  are  used  for  gibs. 
They  are  usually  of  brass  with  babbet,  or  white  metal  inserted  into  grooves 
or  circular  holes. 

On  account  of  the  ease  of  alignment  the  cylindrical  or  turned  gib  is 
generally  used. 


Figs.  257  and  258.— Fishkill-Corliss  crosshead.  The  cylindrical  gibs  are  adjustable  by  means  of 
transverse  eccentric  keys  as  shown  in  the  sectional  end  view.  A  key  is  used  to  secure  the 
piston  rod. 


To  allow  for  wear  between  the  rubbing  surfaces,  gibs  are  made 
adjustable.  There  are  various  methods  of  adjustment,  the 
simplest  of  which  is  the  insertion  of  paper  liners  between  the 
gib  and  crosshead  body. 

Another  mode  of  adjustment  is  by  means  of  inclined  surfaces,  moved  by 
bolts,  or  eccentric  keys. 


♦NOTE. — Cast  iron,  hard  and  close  grained  is  considered  the  best  material  for  guides.  Its 
surface  after  a  few  hours'  work  becomes  exceedingly  hard  and  highly  polished  and  offers  very 
little  resistance  to  the  gib.  So  long  as  this  hard  skin  remains  intact,  no  trouble  will  be  experienced, 
but  if  abrasion  take  place  from  heating  or  other  cause,  it  rarely  works  well  afterwards  and 
should  at  once  be  planed  afresh. 


138 


STEAM  ENGINE  PARTS 


Figs.  2.'9  and  260. — Fulton-Corliss  cross  head._  The  gits  wS,  S,  have  cylindrical  faces,  and  are 
fitted  .to  the  inclined  surfaces  M,  M',  being  adjustable  by  the  nuts  B,  C,  and  B',  C,  on  studs 
A,  A'. 


Fig.  261 .— Reeves-Cubberley  cross 
head  for  vertical  engine  show- 
ing sectional  view  of  wrist  pin 
and  bearing  with  oiling  device. 
In  the  cup  there  is  a  partition 
A,  as  shown,  oil  from  the  vertical 
pipe  fills  the  oil  cup  on  both 
sides  of  the  partition  A.  One 
side  of  the  partition  connects 
with  channel  E,  through  which 
the  top  half  of  the  cross  head  pin 
D,  and  connecting  rod  box  B,  is 
lulDricated.  When  pressure  is 
relieved  between  surface  of  pin 
D,  and  rod  bearing  B,  oil  on  in- 
side of  the  partition  in  cup 
flushes  this  space  with  oil;  with- 
out this  partition  A,  in  the  cup, 
oil  would  settle  to  the  bottom 
of  cup  and  the  top  surface  of 
the  pin  would  not  get  oil  as  it 
now  does.  Of  course,  the  bot- 
tom side  of  cross  head  pin  and 
bearing  C,is  oiled  through  chan- 
nel F,  in  the  manner  described 
above. 


STEAM  ENGINE  PARTS 


139 


There  are  numerous  modifications  of  this  mode  of  adjustment 
as  shown  in  the  accompanying  cuts. 


Fig.  262. — Cross  head  of  Ames  single  valve  engine.  It  is  of  semi-box  section  and  fitted  both  on 
top  and  bottom  with  removable  shoes  spotted  with  babbitt  forming  about  40%  of  the  wearing 
surface.  The  tapered  pin  is  held  in  position  by  four  tap  bolts  passing  through  the  head  of 
the  pin.  By  removing  these  four  bolts  and  replacing  in  tapped  holes  provided  in  the  flange,  the 
pin  may  easily  be  drawn  from  the  cross  head  without  the  use  of  a  sledge,  making  it  possible 
to  remove  and  replace  the  pin  from  the  front  side  of  the  engine.  The  pin  may  be  turned 
90°  when  worn  to  provide  new  wearing  surfaces. 


Fig.  263. — Clyde  hoisting  engine  cross  head  and  guide.  The  cross  head  is  of  the  single  bar 
locomotive  type  and  is  fitted  with  bronze  gibs.  In  reversing  engines^he  cross  heads  are 
furnished  with  bronze  gibs  for  both  top  and  bottom  sides  of  guide  bar.  The  bar,  as  shown,  is 
recessed  at  each  end  to  permit  over-travel  of  the  gib,  thus  preventing  the  wearing  of  shoulders. 
These  recesses  also  retain  the  oil. 


140 


STEAM  ENGINE  PARTS 


The  first  named  method  of  adjustment  by  inclined  surfaces  is  shown  in 
figs.  259  and  260.  The  gibs  S,  S',  rest  on  inclined  surfaces  M,  M',  of  the 
cross  head,  and  by  moving  them  to  the  left  they  will  be  spread  further 
apart.  By  this  means  wear  may  be  taken  up  between  the  rubbing  surfaces. 
A  stud  A,  attached  to  either  side  of  the  cross  head,  passes  through  a  projection 
on  each  gib.  The  gibs  are  retained  in  any  position  by  means  of  these  studs 
and  the  nuts  B,  C,  and  B',  C 


Figs.  264  and  265. — Harris-Corliss  cross  head.  The  gibs  have  V  shaped  faces  with  wedge  ad- 
justment. A  movable,  concealed  wedge  operated  by  the  through  bolt,  permits  the  adjust' 
ment  of  the  gibs  without  any  lengthwise  movement  of  the  latter. 


Figs.  266  and  267. — Split  type  of  cross  head,  and  wrist  pin.  The  neck  is  threaded  to 
receive  the  piston  rod.  Instead  of  the  usual  lock  nut,  the  neck  is  spht,  and  the  two  halves 
made  to  grip  the  rod  by  means  of  cross  bolts  as  shown.  This  type  of  joint  is  satisfactorv 
when  the  machining  is  carefully  done;  a  loose  fit  will  cause  trouble. 


STEAM  ENGINE  PARTS 


141 


To  make  the  adjustment,  nut  B,  is  first  loosened  and  then  nut  C,  tight- 
ened until  the  gib  is  in  the  desired  position,  nut  B,  is  then  tightened  which 
locks  the  gib  in  place. 

There  are  numerous  modifications  of  this  mode  of  adjustment 
as  shown  in  the  accompanying  cuts. 

The  cross  head  shown  in  figs.  264  and  265  has  the  rubbing  surfaces  inclined 
and  the  adjustment  for  wear  is  made  by  concealed  wedges  operated  by 
fore  and  aft  adjusting  bolts. 

Adjustment  by  means  of  eccentric  keys  is  shown  in  figs.  257  and  258.  The 
gibs  are  fitted  with  four  tapered  keys  which  work  crosswise;  the  con- 
struction is  plainly  shown  in  the  two  views. 

Cross  heads  are  attached  to  piston  rods  by  screwed  joints,  or 
by  means  of  keys. 


Figs.  268  and  269. — Eclipse  Corliss  connecting  rod.  The  type  generally  used  on  slow  and 
medium  speed  engines.  The  rod  of  circular  section  tapers  from  the  middle  to  the  forged  ends 
which  contain  the  crank  and  wrist  pin  brasses.  As  constructed,  one  adjustment  lengthens 
the  rod,  while  the  other  shortens  it,  the  combined  effect  is  to  keep  the  length  the  same. 


In  the  first  method,  either  a  lock  nut  is  provided  to  prevent  the  rod 
turning,  or  else  the  neck  of  the  cross  head  is  split  forming  a  split  bushing 
as  shown  in  fig.  266.  The  rod,  after  it  is  screwed  into  the  bushing, 
is  clamped  by  two  bolts  with  lock  nuts.  The  principle  here  employed  being 
the  same  as  with  the  wrist  pin  in  fig.  239.  In  either  case,  first  class  machine 
work  is  necessary  as  more  or  less  trouble  is  experienced  with  a  loose  fit. 

The  Connecting  Rod. — The  to  and  fro  or  reciprocating 
motion  of  the  piston  is  converted  into  a  rotary  motion  by  the 
connecting  rod,  which  joins  the  crosshead  to  the  crank.  The 
connection  is  made  by  the  wrist  and  crank  pins,  for  which  there 
are  suitable  bearings  at  the  ends  of  the  rod. 

The  length  of  the   connecting  rod,   measured  between   the 


142 


STEAM  ENGINE  PARTS 


centers  of  the  wrist  and  crank  pins,  is  usually  two  to  two  and  a 
half  times  the  length  of  the  stroke;  the  latter  proportion,  says 
Thurston,  giving  a  long  and  easy  working  rod,  and  the  former 
a  rather  short,  but  yet  a  manageable  one. 

The  rod  must  be  strong  enough  to  resist  not  only  the  alternate 
stresses  of  tension  and  compression,  but  also  the  bending  stresses 
due  to  its  oscillation. 


^ 


/r-T~^ 


1^1^^'- 


^ 


^ 


Figs.  270  and  271. — Ball  and  Wood  connecting  rod.  This  is  the  form  of  rod  used  on  high  speed 
engines.  The  rectangular  cross  section,  and  the  pronounced  sidewise  taper  is  the  best  shape 
to  resist  the  severe  bending  strains  due  to  high  rotative  speed. 


For  engines  of  slow  and  medium  rotative  speed,  the  rod  is  usually  of 
circular  cross  section,  tapered  from  the  center  to  both  ends  as  shown  in 
figs.  268  and  269. 

In  high  speed  engines,  the  rod  is  made  of  rectangular  section  as  shown 
in  figs.  270  and  271,  which  is  a  better  shape  to  resist  the  bending  strains. 

Most  connecting  rods  are  made  of  steel  while  the  bearings  or 
brasses  are  of  brass  lined  usually  with  Babbitt  metal.  The  rod 
ends  are  solid  or  built  up. 

There  are  various  arrangements  for  adjusting  the  brasses  to 
take  up  wear,  such  as: 


STEAM  ENGINE  PARTS 


143 


1.  Blocks; 

2.  Bolts; 

3.  Gibs  and  cotters. 

Figs.  272  and  273  show  a  solid  end  with  block  adjustment.  A  rectangular 
slot  is  cut  in  the  enlarged  section  in  which  is  inserted  the  brasses  A  and  B, 
having  suitable  flanges  C  and  D,  to  retain  them  in  the  slot.  A  wedge  shaped 
block  E  is  fitted  to  the  slide  upon  B,  thus  bringing  A  and  B  closer  together 
and  reducing  the  size  of  the  bearing.  Two  bolts,  F  and  G,  are  threaded  in 
the  ends  of  the  block  to  secure  it  in  position. 

To  adjust  the  bearing,  F  is  first  loosened  and  then  G  tightened  to  the 
desired  amount.    The  block  is  then  locked  in  place  by  tightening  F. 


v-^ 

-'11^ 

"T^     1 

i  i^ 

f^=^ 

_>--^ 

-^11  .- 

i=^ 

Figs.  272  and  273. — Solid  end  with  block  adjustment;  used  extensively  on  Corliss  connecting 
rods  for  both  the  wrist  pin  and  crank  pin.  The  parts  are:  A,  B,  brasses,  A  being  provided 
with  flanges  C,  D;  E,  adjusting  block  or  wedge;  F,  G,  adjustment  bolts  which  retain  the 
block  in  the  desired  position. 


On  marine  engines  the  adjustment  is  usually  made  by  means  of  bolts 
especially  at  the  crank  end,  as  shown  in  figs.  274  and  275,  on  account  of  the 
ease  with  which  it  is  disconnected  from  the  crank.  The  rod  ends  in  a  T  sec- 
tion A,  upon  which  is  placed  the  brasses  B  and  C  and  an  iron  or  steel  cap  D. 
Two  bolts  E  and  P  pass  through  these  several  members,  securing  them 
firmly  together.    A  set  screw  G  locks  the  bolt  nuts. 

Sometimes  the  set  screw  is  omitted  and  the  two  nuts  provided  for  each 


144 


STEAM  ENGINE  PARTS 


bolt  which  serves  the  same  purpose.     Liners  H,  are  inserted  between  the 
brasses  to  prevent  them  seizing  the  pin  when  the  bolts  are  tightened. 

To  adjust  this  bearing  the  bolts  are  first  loosened  and  then  one  or  more 
liners  removed  or  replaced  as  the  case  may  be,  the  bolts  tightened,  and 
the  nuts  locked  by  the  set  screws. 


()                r 

i\ 

1    ■       ML 

!     4^' 

a 

i     ' 

1/ 

Figs.  274  and  275. — Marine  connecting  rod  with  forked  end  and  double  bearing  for  the  wrist 
pin.     To  the  T  end  A,  is  attached  the  brasses  B,  C,  and  cap  D,  by  the  bolts  E  and  F. 


On  large  bearings,  as  shown  in  fig.  276,  the  brasses  are  hollowed  out  at 
A,  and  B,  to  save  metal,  some  provision  being  made  so  that  the  bolts  will 
not  turn  with  the  nuts.  * 


Fig.  276.— The  Phoenix  connecting  rod.  The  crank  pin  end  is  of  the  marine  type  while  the 
wrist  pin  end  is  solid  with  block  adjustment.  The  illustration  shows  the  arrangement  of 
oil  grooves,  and  the  recesses  in  the  brasses  to  retain  the  Babbitt  lining  in  place. 

*NOTE. — The  bolts  are  usually  turned  with  part  of  their  length  reduced  to  the  diameter 
of  the  bottom  of  the  thread.    This  makes  the  bolt  more  elastic  without  reducing  its  strength. 


STEAM  ENGINE  PARTS 


145 


The  wrist  pin  end  of  a  marine  rod  is  made  in  several  ways. 
It  may  be : 

1.  A  solid  end  with  block  adjustment  as  shown  in  fig.  276; 


"Fig.  277. — Marine  connecting  rod  with  forked  wrist  pin  end;  the  two  branches  carry  the  wrist 
pin. 

2.  A.  forked  end  having  two  arms 
to  which  is  attached  the  wrist  pin 
{^g^  277);. 

3.  A  forked  end  carrying  two 
wrist  pin  bearings,  as  shown  in 
figs.  274  and  275. 

In  the  second  mentioned  construction 
it  should  be  noted  that  the  wrist  pin 
is  made  fast  to  the  rod  instead  of  to  the 
crosshead.  This  requires  that  the  cross- 
head  contain  the  bearing. 

Many  marine  engines  of  the  smaller 
sizes  have  this  type  of  rod  end.  Figs. 
279  to  281  show  the  style  crosshead 
used  with  rod  in  position. 

In  figs.  282  and  283  is  shown  a  built  up 
rod  end  with  gib  and  cotter  adjustment.* 
The  rod  end  A  which  is  of  enlarged  rec- 
tangular cross  section  and  the  brasses 


Fig.  278. — Marine  connecting  rod  with  forked  wrist  pin  end,  containing  a  double  bearing  for 
the  wrist  pin.  The  advantage  of  this  form  of  rod  is  that  the  height  of  the  cyUnders  may- 
be less  than  with  other  types;  it  is  difficult,  however,  to  make  uniform  adjustment  of  the 
two  bearings. 


^OT'S.— Continued. 

hence,  it  is  better  able  to  resist  the  severe  shocks  that  come  upon  it.  To  provide  for  uneven 
adjustments  each  bolt  is  made  large  enough  to  carry  two-thirds  of  the  load  and  so  pro- 
portioned that  the  stress  on  it  does  not  exceed  5,000  pounds  per  square  inch  at  the  smallest 
cross  section.  Since  in  adjusting  the  bolts  more  pressure  is  liable  to  be  brought  on  one  than 
the  other,  two-thirds  of  the  load  should  be  considered  as  being  carried  by  one  bolt  in  determining^ 
its  size. 


146 


STEAM  ENGINE  PARTS 


liiOl 


Figs.  279  to  281. — Detail  of  connecting  rod  with  wrist  pin  in  forked  end  and  cross  head  contain- 
ing wrist  pin  bearing. 


?IGS.  282  and  283. — Built  up  connecting  rod  with  gib  and  cotter  adjustment.     The  parts  are: 
A,  stub  end  of  rod;   B  and  C,  brasses;   D,  strap;   E  and  F,  cotters;   G,  gib;   H,  set  screw. 


STEAM  ENGINE  PARTS 


147 


B  and  C  are  held  together  by  a  strap  D,  two  cotters  E  and  P  and  the  gib  G.  * 
The  latter  is  a  wedge  shaped  key,  which  on  being  driven  in,  forces  the 
strap  to  the  right,  thus  bringing  the  brasses  closer  together.  The  gib  is 
retained  in  the  desired  position  by  the  set  screw  H.  . 

Sometimes  the  cotters  E  and  P  are  omitted  and  the  strap  fastened  to 
the  rod,  as  shown  in  figs.  284  and  285,  by  the  bolts  A  and  B.  The  brasses 
are  adjusted  by  the  gib  G  which  has  a  threaded  end  and  nut  C.  At  E  is 
shown  a  wiper  oil  cup. 


U-UlLULGj 


Figs.  284  and  285. — Built  up  connecting  rod  cotters.  The  cross  bolts  A  and  B  secure  the  strap 
to  the  stub  end  of  the  rod.  The  gib  G  is  adjusted  at  the  stud  end  C.  A  wiper  oil  cup  for  a 
horizontal  rod  is  shown  at  E . 


Two  other  methods  of  gib  adjustment  are  shown  m  figs.  286  and  287. 
In  each  case  the  gib  is  attached  to  a  bolt;  in  fig.  286  the  bolt  forms  a  part 
of  the  cotter,  and  in  fig.  287  the  cotter  is  omitted,  the  bolt  being  threaded 
into  the  rod  end. 


*NOTE. — The  thickness  of  the  gib  or  key  is  usually  one-fourth  of  the  width  of  the  strap, 
and  the  breadth  parallel  to  the  strap  should  be  such  that  the  cross  section  will  hav^e  a  shearing 
strength  equal  to  the  tensile  strength  of  the  section  of  the  strap.  The  taper  of  the  gib  is  gen- 
erally about  five-eighths  inch  to  the  foot. 


148 


STEAM  ENGINE  PARTS 


If,  9,s  a  result  of  adjusting  the  brasses  of  a  connecting  rod,  its 
length  be  changed,  the  clearance  at  the  two  ends  of  the  cylinder 
will  be  altered. 


Figs.  286  and  287. — Two  methods  of  gib  adjustment, 
forms  part  of  the  cotter;  fig.  287,  cotter  omitted. 


Fig.  286. — Gib  attached  to  bolt  which 


To  prevent  this,  the  rod  is  sometimes  constructed  in  such  a  way  that 
tightening  up  the  brasses  at  one  end  lengthens  the  rod,  and  tightening  at 
the  other  end  shortens  it  as  shown  in  fig.  288,  where  taking  up  wear  at 
the  crank  pin  end  pushes  the  outer  brass  in  and  shortens  the  rod,  while  a 

rm 


Fig.  288. — Twin  City  CorHss  connecting  rod  with  soHd  ends  and  block  adjustment.  The 
blocks  or  adjusting  wedges  are  on  the  same  side  of  the  pins,  thus  tending  to  maintain  a 
constant  length  of  rod. 

similar  adjustment  at  the  wrist  pin  end  moves  the  inner  brass  outward 
and  lengthens  the  rod.  Thus,  the  effect  of  the  two  adjustments  tends  to 
keep  the  rod  length  the  same. 


A  modification  of  the  solid  end  rod  is  shown  in  fig.  287,  which 


STEAM  ENGINE  PARTS 


149 


is  a  desirable  rod  for  a  large  engine;   it  is  known  as  the  "hatchet 
end"  type. 

By  this  arrangement,  when  the  bolt  is  removed  from  its  position  it  allows 
a  side  of  the  strap  to  be  taken  out,  so  that  the  rod  can  be  easily  lifted  off 


Fig.  289. — The  "hatchet"  end  type  of  connecting  rod  as  used  on  the  Harris-Corliss  engine. 
A  desirable  form  for  large  engines,  permitting  easy  removal  of  the  brasses. 

the  pin.     The  adjustment  of  the  brasses  is  made  by  means  of  concealed 
blocks,  set  up  by  adjusting  bolts. 

On  some  rods  the  end  is  made  removable  instead  of  the  side.    A  rod  of 
this  kind  is  shown  in  fig.  290.    The  block  A  at  the  end  is  dovetailed  to  fit 


Pig.  290.-; — Connecting  rod  of  the  Ames  engine.  The  extreme  end  is  a  separate  piece  removable 
by  taking  out  the  end  bolts.  The  brasses  are  then  easily  accessible.  The  rod  is  provided 
with  block  adjustment. 

the  ends  of  the  fork  and  is  held  in  place  by  a  large  bolt  as  shown.  By  re- 
moving the  bolt  and  block,  the  bearing  may  be  taken  out  from  the  rod 
for  inspection  without  disturbing  the  adjustment. 


In  single  acting  engines  it  is  not'  considered  necessary  by  some 
to  use  refined  methods  of  taking  up  wear. 


150 


STEAM  ENGINE  PARTS 


Fig.  291  shows  the  connecting  rod  used  on  the  larger  sizes  of  Westing- 
house  vertical  single  acting  engine,  no  special  provision  being  made  for  ad- 
justment. 


Fig.  291. — The  Westinghouse  connecting  rod  for  high  speed,  short  stroke  engines.  On  account 
of  the  large  cyhnder  diameter  in  proportion  to  the  stroke,  the  bearings  are  of  unusual  size 
for  the  length  of  rod. 

The  strap  is  held  rigid  in  place  by  two  tap  bolts  passing  through  the  rod 
end  and  threaded  into  one  side  of  the  strap.  The  bronze  bearings  are  lined 
with  Babbitt  metal  and  are  kept  in  place  sidewise  by  flanges  which  embrace 
the  sides  of  the  strap  and  rod. 

When  lost  motion  becomes  unusually  large  it  may  be  taken  up  by  in- 
serting between  the  stub  end  of  the  rod  and  the  bronze,  one  or  more  pieces 
of  thin  sheet  steel  known  as  shims  or  liners. 


Fig.  292  illustrates  the  general  proportion  of  a 
rod  suitable  for  a  short  stroke  high  speed  engine. 

The  rod  ends  are  very  large  in  proportion  to  the 
length  of  the  rod.  This  results  from  the  large  cylinder 
diameter  as  frequently  in  engines  of  this  class,  the 
diameter  is  greater  than  the  length  of  the  cylinder, 
and  the  length  of  the  rod  with  respect  to  the  stroke  is 
usually  less  than  for  ordinary  service. 

Ques.    What  is  a  * 'gudgeon"? 

Ans.     A  gudgeon  is  an  obsolete  name  for  a 
wrist  pin. 


Fig.  292. — Sturtevant  connecting  rod  for  vertical  singie  engine.  The  rod  is  an  open  hearth 
steel  forging.  The  marine  type  crank  pirt  box  is  of  babbitted  malleable  iron  or  semi-steel, 
dependent  on  size.  The  wrist  pin  box  is  also  of  the  marine  type,  except  in  the  larger  sizes, 
which  are  of  the  solid  end  type  with  wedge  adjvstment. 


STEAM  ENGINE  PARTS 


151 


Oues.  Is  the  full  force  exerted  on  the  piston  trans- 
mitted to  the  crank? 

Ans.  Only  at  the  dead  centers.  At  any  other  point  of  the 
stroke,  part  of  the  force  is  transmitted  as  a  side  thrust  to  the 
guides. 

Oues.  When  a  force  is  thus  divided  into  two  or  more 
forces  acting  in  different  directions  what  are  they  called  ? 


Fig.  293. — Parallelogram  of  forces  showing  the  two  component  forces  at  the  crosshead  due  to 
the  thrust  of  the  piston.  By  means  of  this  diagram  the  pressure  on  the  guides  and  on  the 
crank  pin  can  be  obtained. 


Ans.     Components.     The  original  force  is  called  the  resultant 
because  it  is  the  equivalent  of  the  several  component  forces. 

Oues.     How  may  component  forces  such  as  those  pro- 
duced by  the  action  of  a  connecting  rod  be  measured  ? 

Ans.     By  drawing  a  parallelogram  of  forces  as  in  fig.  293. 

In  the  skeleton  diagram  of  the  moving  parts  of  an  engine,  the  line  of  the 
piston  is  extended,  and  with  any  suitable  scale  the  distance  A  B  marked 
off  so  that  it  will  represent  the  total  load  on  the  piston. 

For  instance,  if  the  total  load  on  the  piston  be  500  pounds,  and  the  scale 
taken  be  100  pounds  to  the  inch,  then  A  B  will  be  five  inches. 

At  A,  the  center  of  the  wrist  pin,  the  force  transmitted  to  the  piston  rod^ 
by  the  piston  will  split  up  into  two  component  forces,  one  acting  in  the 
direction  of  the  connecting  rod  and  the  other  acting  perpendicular  to  the 


152  STEAM  ENGINE  PARTS 


guide.  The  intensity  of  these  forces  is  found  by  drawing  Hnes  through  B, 
parallel  to  the  directions  in  which  they  act,  giving  the  points  C  and  D.  By 
measuring  A  C  and  A  D,  with  the  same  scale  as  was  used  in  laying  off  A  B, 
-and  multiplying  by  the  pounds  per  inch  the  intensity  of  the  forces  is 
obtained. 

The  thrust  on  the  guide,  when  the  connecting  rod  is  at  its  maximum  angle 
with  the  axis  of  the  piston  rod,  may  also  be  found  by  the  formula: 

Thrust  =^  tan  ^ 
in  which 

p  =  total  load  on  the  piston, 
B  =  maximum  angle  of  connecting  rod 
The  angle   0,  is  the  angle  whose  sine  =  3^  stroke  of  piston -i- length  of 
connecting  rod.    Its  values  for  rods  of  different  lengths  are: 

Ratio  of  length  of  connecting  rod  to  stroke  2  23^2  3 

Maximum  angle  of  the  connecting  rod         14°  29'       11°  33'       9°  36' 
Tan  e  .258  .204         .169 

Example. — If  the  total  load  on  the  piston  be  5,000  lbs.,  and  the  length 
of  the  rod  be  2H  times  the  stroke,  then  the  maximum  thrust  on  the  guide  is: 
5,000 X.204  =  1,020  lbs. 

Oues.  How  does  the  thrust  of  the  connecting  rod  act 
on  the  crank  pin? 

Ans.  It  is  split  up  into  two  component  forces.  One  acts  in 
the  direction  of  a  tangent"^  to  the  circle  described  by  the  crank 
pin  which  causes  the  crank  to  turn,  and  the  other  acts  in  the 
direction  of  the  axis  of  the  crank  arm  which  causes  the  shaft 
to  press  against  its  bearing. 

Thus,  in  fig.  294,  the  thrust  of  the  connecting  rod  is  split  up  at  A,  into  two 
component  forces,  one  acting  in  the  direction  of  the  tangent  A  M,  and  one 
in  the  direction  of  the  axis  A  O.  By  laying  off  A  B,  equ-al  to  the  thrust  of 
the  connecting  rod,  and  completing  the  parallelogram  of  forces,  the  points 
C  and  D,  are  obtained  giving  the  lines  A  C  and  A  D,  whose  lengths  repre- 
sent the  intensity  of  these  forces. 

Oues.    What  is  the  component  A  C,  called? 

•  Ans.     The  tangential,  or  turning  force. 


*N0TE. — A  tangent  to  a  circle  is  a  straight  line  drawn  through  a  point  on  its  circum- 
ference and  perpendicular  to  a  line  joining  this  point  at  the  center.     . 


STEAM  ENGINE  PARTS  153 

Oues.     What  is  the  nature  of  this  turning  force? 

Ans.  It  is  always  less  than  the  force  acting  on  the  piston. 
It  increases  from  zero  at  the  dead  center  to  a  maximum  near 
the  center  of  the  stroke  and  then  diminishes  to  zero  at  the  end 
of  the  stroke. 

Oues.  Since  the  turning  force  is  always  less  than  the 
force  acting  on  the  piston,  is  there  not  a  considerable  loss 
of  power  caused  by  this  peculiar  action  of  the  connecting 
rod? 


Pl5T0^4 


CROSS 

PISTON  ROD  HI 


Fig.  294. — Parallelogram  of  forces  showing  the  two  component  forces  at  the  crank  pin.  By- 
means  of  this  diagram  the  tangential  force  or  "turning  effect"  can  be  obtained  for  any- 
crank  position. 

Ans.  No.  Neglecting  friction,  the  same  amount  of  work 
that  is  done  on  the  piston  is  delivered  to  the  crank  pin  by  the 
connecting  rod  in  turning  the  shaft. 

Oues.     Why  is  there  no  loss  of  power? 

Ans.  Because  during  each  stroke,  the  crank  pin  travels  a 
greater  distance  than  the  piston.  Hence,  the  smaller  turning 
force  by  acting  through  a  longer  distance,  does  the  same  amount 
of  work  as  the  larger  force  on  the  piston  acting  through  the 
shorter  distance. 

Work  is  the  product  of  two  factors:   force  and  distance  through  which 
the  force  acts.     These  two  factors  are  inversely  proportional  for  a  given 


154 


STEAM  ENGINE  PARTS 


amount  of  work;  that  is,  if  one  factor  be  increased,  the  other  is  diminished 
a  Hke  amount.  For  instance,  to  raise  one  pound  ten  feet  requires  the  same 
amount  of  v/crk  as  is  required  to  raise  ten  pounds  one  foot,  or  two  pounds 
five  feet. 

Now,  in  a  steam  engine,  while  the  crank  pin  is  revolving  at  a  constant 
tangential  speed*,  the  speed  of  the  piston  is  ever  varying. 

Oues.     What  is  the  nature  of  the  motion  of  the  piston? 

Ans.  It  starts  from  rest  at  the  beginning  of  the  stroke, 
increasing  to  a  maximum  near  the  middle,  then  diminishes  until 
it  again  comes  to  rest  at  the  end  of  the  stroke. 


-M 

FORWARD 


3^V  R' 


Fig.  295. — Diagram  showing  the  effect  of  the  angularity  of  the  connecting  rod.  For  equal 
crank  pin  movement  from  each  end  of  the  stroke,  the  angularity  of  the  rod  causes  the  piston 
to  travel  further  on  the  forward  stroke,  than  on  the  return  stroke. 

The  conditions  which  prevail  at  the  piston  and  crank  pin  clearly  illus- 
trate the  inverse  relations  which  exist  between  the  factors /orce  and  distance 
for  a  given  amount  of  work  as  can  be  shown  by  a  series  of  diagrams. 


Owes.  What  effect  does  the  connecting  rod  have  on  the 
movement  of  the  piston? 

Ans.  Starting  at  the  beginning  of  the  forward  stroke,  the 
inclination  or  angularity^  of  the  rod  with  respect  to  the  cylinder 
axis,  causes  the  piston  to  move  somewhat  more  than  half  its 


*NOTE. — The  tangential  speed  of  a  point  revolving  in  a  circle  is  its  equivalent  speed  if 
it  were  moving  in  a  straight  line.  Thus,  the  speed  of  a  belt  as  it  leaves  a  pulley  is  the  tan- 
gential speed  of  a  point  on  the  face  of  the  pulley. 

fNOTE.^ — The  "angularity"  of  the  connecting  rod  is  sometimes  called  the  obliquity. 


STEAM  ENGINE  PARTS  i  155 

stroke  while  the  crank  is  moving  the  first  quarter  of  its  revolution, 
somewhat  less  than  half  stroke  during  the  second  and  third 
quarters,  and  again  somewhat  more  than  half  stroke  during  the 
fourth  or  last  quarter  of  the  revolution. 

In  fig.  295  is  shown  the  effect  of  the  angularity  of  the  rod  in  distorting 
the  movement  of  the  piston.  In  the  diagram  the  piston  is  not  shown 
since  its  position  with  respect  to  the  stroke  corresponds  exactly  to  that  of 
the  wrist  pin  C. 

The  connecting  rod  is  shown  in  two  positions,  C  R  and  C  R',  such  that 
the  crank  pin  has  traveled  equal  distances  A  R  and  B  R'  from  the  dead 
centers.  The  piston  positions  are  indicated  by  C  and  C\  the  piston  having 
traveled  on  the  forward  stroke  the  distance  M  and  on  the  return  stroke  the 
distance  S.  For  equal  crank  pin  travel  from  each  end  of  the  stroke,  it  is 
thus  seen  that  the  piston  travels  further  on  the  forward  stroke  than  on 
the  return  stroke 

Were  it  not  for  the  angularity  of  the  rod,  the  piston  would  travel  the 
equal  distance  M'  and  S'.  The  connecting  rod  then  increases  the  piston 
travel  by  a  distance  N  C  on  the  forward  stroke  and  diminishes  it  by  a  dis- 
tance N'  C  on  the  return  stroke. 

Oues.     On  what  does  the  amount  of  this  distortion  of 
the  pistdh  movement  depend? 

Ans.     On  the  length  of  the  connecting  rod. 

The  shorter  the  rod  the  greater  the  distortion. 

Oues.    What  important  effect  has  the  angularity  of  the 
rod  on  the  steam  distribution  to  the  cylinder? 

Ans.     It  causes  cut  off  to  occur  too  late  on  the  forward  stroke, 
and  too  soon  on  the  return  stroke. 

Ques.    What  is  a  ''Scotch  yoke?" 

Ans.     A  device  sometimes  used  instead  of  a  connecting  rod. 

It  consists  of  a  metal  frame  similar  to  a  Stevenson  link  but  with  straight 
sides  as  shown  in  fig.  298.  To  the  center  of  one  side  is  attached  the  piston 
rod.  A  continuation  of  the  rod  from  the  other  side  passes  through  a  bearing 
which  prevents  any  side  movement  of  the  yoke.  The  crank  pin  passes 
through  a  block  which  slides  to  and  fro  in  the  yoke. 


156 


STEAM  ENGINE  PARTS 


Oues.    What  are  the  advantages  of  a  Scotch  yoke? 

Ans.  There  is  no  distortion  in  the  piston  movement  and  the 
crank  shaft  may  be  placed  nearer  the  cyHnder  than  with  a 
connecting  rod.    . 

Oues.  Why  then  has  it  been  displaced  by  the  con- 
necting rod  ? 

Ans.  Because  the  good  features  of  a  Scotch  yoke  are  more 
than  offset  by  the  friction  and  wear  of  the  block  and  by  the 
extended  piston  rod  and  outer  bearing. 


SCOTCH   YOKE 


Fig.  296. — The  "Scotch  yoke."  Used  to  some  extent  on  early  engines.  Its  advantages  are 
overbalanced  by  several  objections,  such  as  friction  and  wear  of  block,  extended  piston  rod, 
outer  bearing,  etc. 

The  Crank  Shaft. — The  to  and  fro,  or  reciprocating  motion 
of  the  piston  is  converted  into  rotary  motion  by  the  crank  shaft 
which  consists  of: 

1.  The  shaft; 

2.  The  crank  arm; 

3.  The  crank  pin. 

In  construction,  the  crank  shaft  is  either  built  up  from  separate 
parts  or  made  from  a  solid  forging. 

According  to  the  type  of  engine,  it  may  be  classified  as: 


STEAM  ENGINE  PARTS 


157 


1.  Overhung  crank;       • 

2.  Center  crank; 

3.  One,    two   or    more    throw   according   to   the    number   of 
cylinders. 


KETVWAVlBEAieiNG  | 

I  \ 


KCYWAV 


I  I 

I   BC./\f?ING| 

I  i 

Fig.  297.; — Usual  form  of  shaft  for  a  stationary  engine.  The  crank  arm  is  fitted  to  the  end  A, 
which  is  turned  to  slightly  reduced  diameter.  The  keyway  in  the  central  portion  is  for  the 
fly  wheel. 


In  the  built  up  type  as  generally  used  on  stationary  engines, 
the  shaft  itself  consists  of  a  cylindrical  piece  of  suitable  length 
as  shown  in  fig.  297. 

A  portion  of  the  shaft,  A,  upon  which  the  crank  is  fastened  is  sometimes  . 
turned  to  slightly  smaller  diameter,  thus  forming  a  shoulder  against  which 
.  the  crank  is  driven  when  being  fitted.  The  length  B  is  made  such  that  there 
is  sufficient  room  for  the  bearings,  valve  gear  and  fly  wheel.  Two  keyways 
are  provided,  as  shown  in  the  figure,  so  that  the  crank  and  the  fly  wheel 
may  be  keyed  to  the  shaft  and  thus  prevented  turning  on  the  latter. 


ri_V  WHEEL. 


I  BEWRINq 


Fig.  298.— Approved  form  for  a  long  shaft  carrying  a  heavy  fly  wheel.     The  enlarged  central 
portion  gives  stiffness  to  prevent  springing. 


On  an  engine  having  a  heavy  fly  wheel  and  long  shaft,  it  is 
usual  to  make  part  of  the  shaft  tapered  as  shown  in  fig.  298. 
This  gives  great  strength  to  resist  bending  stresses. 


158 


STEAM  ENGINE  PARTS 


In  some  cases,  instead  of  reducing  the  shaft  diameter  for  the  crank  as 
in  fig.  297,  a  shoulder  is  formed  by  a  projection  or  flange  as  shown  in 
fig.  299. 

The  crank  consists  of  an  arm  with  a  boss  at  each  end,  one  to  take  the 
main  shaft  and  the  other  the  crank  pin.  The  arm  is  made  soHd,  or  of  webbed 
cross  section  as  shown  in  figs.  300  and  301. 


Fig.  299. — Crank  end  of  shaft  with  flange  instead  of  shoulder, 
diameter  of  the  shaft  is  not  reduced  at  the  crank  end. 


With  this  construction  the 


The  crank  is  secured  firmly  on  the  shaft  by  making  it  a  drive  or  shrink 
fit  and  further  secured  by  a  key.  * 

The  shrinking  is  done  by  boring  out  the  hole  a  shade  smaller  than  the 
shaft,  then  heating  the  crank  around  the  hole,  thus  causing  the  material 
to  expand  and  the  hole  to  become  larger.  The  crank  is  then  placed  on  the 
shaft,  and  on  cooling  it  contracts  and  grips  the  shaft  with  great  firmness. 


Figs.  300  and  301. — Webbed  crank  arm.  The  crank  is  usually  fastened  to  the  shaft  with  a 
drive,  or  shrink  fit,  and  further  secured  by  a  key.  The  parts  shown  are:  A,  shaft;  B, 
webbed  crank  arm;    C,  crank  pin;   D,  boss  at  shaft  end;    D',  boss  at  pin  end;   E  key. 


The  crank  pin  is  usually  forced  in  place  by  hydraulic  pressure,  or  fitted 
by  shrinkage  and  the  end  riveted  as  at  D'  in  fig.  300;  as  a  rule  no  key  is 
provided. 

The  proportions  between  the  diameter  and  length  of  the  crank  pin  vary. 


*NOTE. — The  standard  proportions  for  a  key  are:    width  =>^  of  the  shaft  diameter, 
thickness  =  }i  of  the  shaft  diameter. 


STEAM  ENGINE  PARTS 


159 


On  slow  running  engines  long  pins  may  be  used  to  advantage,  but  high 
speed  engines  require  short  pins  in  order  to  bring  the  pin  closer  to  the 
main  bearing  and  thus  reduce  the  bending  stresses  set  up  by  the  inertia 
of  the  connecting  rod.  It  should  be  noted  that  for  a  crank  pin  of  given 
bearing  area,*  the  longer  the  pin,  the  cooler  will  it  run.  This  is  because  the 
smaller  the  diameter,  the  slower  the  speed  of  rubbing. 

The  way  in  which  cranks  are  shrunk  on  to  crank  pins  and 
crank  shafts  is  often  objectionable  and  responsible  for  many 
subsequent  failures,  both  of  shaft  and  crank  pin. 


Pigs.  302  and  303.— Two  forms  of  crank  pin.  The  first  is  objectionable  in  that  the  sharp 
edge  of  the  hole  in  the  crank  arm  may  cut  into  the  pin  and  start  a  crack.  This  danger  is 
avoided  by  the  construction  shown  in  fig.  303. 


Where  a  shoulder  is  provided  as  shown  in  fig.  302,  the  result  is  that 
when  the  crank  is  shrunk  into  position  on  the  pin  or  shaft,  as  the  case  may 
be,  the  sharp  edge  of  the  hole  in  the  crank  cuts  into  the  material  with  a 
shearing  action  and  starts  a  crack  which  afterwards,  under  the  influence 
of  alternating  stresses,  develops  into  a  fracture,  and  frequently,  as  ex- 
perience has  shown,  leads  to  a  serious  breakdown.  To  avoid  this,  the 
crank  and  shaft  may  be  constructed  as  shown  in  fig.  303,  the  part  which  is 
shrunk  on  the  crank  being  of  slightly  larger  diameter  and  of  a  length 
exactly  equal  to  the  thickness  of  the  crank,  so  that  the  shrinkage  of  the 


*NOTE. — The  size  of  the  crank  pin  should  be  such  that  the  pressure  per  square  inch  of 
projected  bearing  area  (that  is,  the  diameter  multiplied  by  the  length)  should  not  exceed 
300  to  400  pounds  for  stationary  engines,  400  to  500  pounds  for  marine  engines  and  800  to  900 
pounds  for  paddle  wheel  engines. 


160 


STEAM  ENGINE  PARTS 


crank  has  no  tendency  to  cut  into  the  material  and  so  start  an  incipient 
fracture. 

The  radius  of  the  crank  arm  is  measured  from  the  center  of 
the  shaft  to  the  center  of  the  crank  pin.  The  throw  of  the  crank 
is  equal  to  the  diameter  of  the  crank  pin  path,  that  is,  the  stroke 
of  the  piston. 


Pig.  304, — Built  up  crank  shaft  of  the  Rollins  engine.    The  crank  pin  is  carried  by  a  disc  which 
is  counter-balanced.    Hydraulic  pressure  is  used  to  force  the  pin  and  shaft  in  place. 

Built  up  crank  shafts  are  sometimes  constructed  with  a  cast 
iron  disc  instead  of  a  crank  arm  as  shown  in  fig.  304. 

The  portion  of  the  disc  opposite  the  pin  is  usually  made  thicker  than 
the  other  part,  the  extra  weight  being  used  as  a  balance  to  the  weights  of 
the  reciprocating  parts  and  known  as  a  counter-weight.  In  high  speed  engines 
this  is  desirable  to  reduce  vibration.  The  disc  is  attached  to  the  shaft  by 
the  methods  just  described. 


The  center  crank  shaft  is  usually  composed  of  two  lengths 


STEAM  ENGINE  PARTS 


161 


of  shaft,  each  provided  with  a  disc  or  arm  and  having  one  crank 
pin  joining  the  two,  as  shown  in  fig.  305. 

This  is  the  construction  usually  found  in  stationary  engines. 

In  the  higher  class  of  engine  construction,  the  crank  shaft  is  made  from 
a  solid  forging  for  the  small  and  medium  sizes,  the  rough  forging  as  de- 
livered from  the  forge  hammer  has  the  form  as  shown  in  fig.  306.  The  crank 
is  first  slotted  out  (fig.  307),  then  turned  in  the  lathe  and  finished  as  shown 
in  fig.  308.  When  counter-weights  are  provided,  they  are  usually  made 
separate  and  clamped  to  the  crank  arms. 


c 

c 

0  \r^t^'s\ 

p 

Fig.  305. — Built  up  crank  shaft,  consisting  of  two  shaft  lengths  S,  S';  two  cranks  C,  C,  and  a. 
crank  pin  P.  In  the  built  up  crank  shaft  the  pieces  are  usually  fitted  together  by  shrinking 
and  keying. 


Pigs.  303  to  308. — Construction  of  a  forged  center  crank  shaft.  Fig.  306  shows  the  rotifli 
forging.  It  is  first  placed  in  a  slotting  machine  which  removes  the  metal  between  the  crank 
arras,  as  in  fig.  307,  and  then  turned  in  a  lathe  and  finished  as  shown  in  fig.  308. 


162 


STEAM  ENGINE  PARTS 


Fig.   309   shows  a  forged  crank  shaft   with   counter-weights  attached 
by  transverse  bolts.    There  are  various  methods  of  attaching  these  weights. 

In  figs.  310  and  312,  the  discs  have  V  shaped  grooves  in  the  side 


Fig.  309. — Crank  shaft  of  the  Erieco  engine  having  counterweights  attached  by  transverse 
bolts. 


Figs.   310  and  312. — Crank  shaft  of  the  Watertown  engine.    The  counter  balance  discs  are 
fitted  to  V  shaped  grooves. 


Fig.  313. — Crank  shaft  assembly  of  Watertown  engine,  shown  disassembled  in  figs.  310  to  312. 


STEAM  ENGINE  PARTS 


163 


164 


STEAM  ENGINE  PARTS 


Figs.  314  and  315  show  a  two  throw  crank  shaft  for  a  compound  engine, 
and  figs.  316  and  317  a  three  throw  for  a  triple  expansion  engine.  The 
former  has  its  cranks  set  at  90^  and  the  latter  at  120°.  The  order  of  the 
crank  positions  is  called  the  sequence  of  cranks. 


Crank   shafts   for   marine    engines,    when    about    10    inches 
diameter  are  generally  -made  in  duplicate  halves,  so  that  in  case 


Fig.  318. — Duplicate  section  for  large  multi-cylinder  crank  shaft. 


Fig.  319.— Taper  flange  bolts  for  connecting  sections  of  large  built  up  crank  shafts.     The 
absence  ot  a  hexagonal  head  improves  the  appearance  of  the  joint. 

of  damage  to  a  part  only  half  the  shaft  is  condemned,  and  a 
spare  half  shaft  can  be  carried  on  foreign  voyages. 

By  this  plan  there  is  less  labor  replacing  the  damaged  half  than  if  the 
whole  shaft  be  moved. 


STEAM  ENGINE  PARTS  165 


•  Flange  couplings  are  usually  provided  at  both  ends,  so  as  to  be  reversible 
in  case  of  a  flaw  showing  near  the  after  end.  Crank  arms  are  forged  with 
the  shaft  ends,  or  shrunk  on  and  keyed.  The  pins  are  usually  shrunk  into 
eyes  in  the  arms. 

Large  crank  shafts  are  usually  built  up  from  duplicate  sections,  there 
being  a  section  for  each  crank  These  have  flange  connections  as  shown  in 
fig.  318.  The  several  sections  being  connected  by  ordinary  bolts  or  taper 
bolts  as  shown  in  fig  319.  The  latter  type  of  bolt  requires  no  head,  thus 
giving  the  flange  connections  a  less  clumsy  appearance. 


The  Main  Bearings. — These  are  the  bearings  in  which  the 
crank  shaft  turns  as  distinguished  from  other  bearings  of  the 
engine.  The  object  of  the  main  bearings  is  to  support  the 
weight  of  the  shaft  and  fly  wheel,  and  to  hold  the  former  in 
place  at  right  angles  to  the  axis  of  the  cylinder,  also  to  receive 
the  pressure  due  to  that  portion  or  component  of  the  thrust 
in  the  connecting  rod  which  is  not  spent  in  turning  the  crank.* 

The  three  requirements  of  a  bearing  are: 

1.  That  it  be  of  such  size  that  the  pressure  of  the  shaft  on 
each  square  inch  of  the  bearing  will  be  sufficiently  low  to  prevent 
heating ; 

2.  That  there  be  means  of  conveying  oil  to  tHe  rubbing  sur- 
faces; 

3.  Provision  for  adjusting  the  bearing  to  take  up  wear. 

A  simple  bearing  consists  of  a  box,  cap,  two  brasses,  liners 
and  bolts  to  hold  the  parts  together.  This  kind  of  bearing  is 
used  on  vertical  engines  as  shown  in  fig.  320. 

The  upper  bearing  surface  or  brass  B  is  let  into  lower  brass  B',  B  being 
fitted  into  a  cap  C.  Both  brasses  are  kept  from  turning  by  dowel  pins  D 
and  D'.  The  brasses  are  cut  away  at  L  and  L'  and  the  space  filled  with 
thin  strips  of  sheet  metal  or  liners;  these,  together,  with  the  brasses  are 
held  firmly  in  place  by  the  bolts  M  and  M'. 


*NOTE. — This  force  was  explained  in  the  section  on  connecting  rods. 


166 


STEAM  ENGINE  PARTS 


A  small  hols  O,  is  drilled  through  the  cap  and  upper  brass  to  convey  oil 
from  the  lubricating  device  to  the  bearing  and  shaft. 

Adjustment  for  wear  is  made  by  taking  off  the  upper  bearing  and  re- 
moving one  or  more  liners  from  each  side.       The  cap  is  then  replaced  and 


/^  v^     "v^  s 


I'iG.  320.— ;-Main  bearing  for  a  vertical  engine;    adjustable  by  means  of  the  bolts  and  liners 
on  the  sides. 


Fig.  321. — Main  bearing  with  liner  adjustment  for  a  horizontal  engine.  The  brasses  ar3 
divided  obliquely  so  that  the  resultant  thrust  of  ^he  shaft  will  come  centrally,  and  not 
at  the  joints. 


STEAM  ENGINE  PARTS 


167 


the  parts  again  firmly  bolted  together.     Some  of  the  liners  are  very  thin 
so  that  adjustment  may  be  made  with  precision. 

This  form  of  bearing  is  sometimes  used  on  horizontal  engines,  in  which 
case  the  brasses  are  divided  obliquely  instead  of  horizontally,  so  that  the 
resultant  thrust  of  the  shaft  will  press  against  the  brasses  centrally  and 
not  in  the  direction  of  the  liners.     This  construction  is  shown  in  fig.  321. 

The  type  of  bearing  just  described  is  called  a  two  piece  hearing 


ENGINE   FRAME 
6 


Fig.  322. — ^A  "four  piece"  main  bearing,  as  generally  used  on  Corliss  and  other  horizontal 
engines.  There  are  two  side  brasses  A  and  B,  an  upper  brass  C,  and  a  lower  brass  D.  Owing 
to  the  great  weight  of  the  wheel,  little  or  no  pressure  comes  on  the  upper  brass  C.  The 
greatest  wear  comes  on  the  side  brasses,  which  are  adjusted  by  means  of  the  wedges  E', 
and  F. 


in  distinction  from  the  more  complicated  form,   or  four  piece 
hearing  as  generally  used  on  horizontal  engines. 

In  this  bearing  the  brasses  are  divided  into  four  parts,  because,  on  medium 
and  low  (rotative)  speed  horizontal  engines,  having  large  and  heavy  fly 
wheels,  the  resulting  pressure  of  the  shaft  on  the  bearing  is  practically  in 
a  horizontal  direction.  Hence,  in  order  to  have  this  pressure  come  centrally 
on  a  brass  instead  of  at  the  junction  of  two  brasses,  they  are  arranged  as 
shown  in  fig.  322. 


168 


STEAM  ENGINE  PARTS 


A  and  B,  are  two  side  brasses,  and  C  and  D,  upper  and  lower  brasses. 
C  and  D,  are  made  long  enough  so  that  at  their  extremities,  they  rest  upon 
A  and  B ;  hence,  by  means  of  the  two  adjustable  bolts  1  and  2,  the  four 
brasses  are  prevented  moving  in  a  vertical  direction,  the  cap  being  secured 
by  the  bolts  5  and  6.  The  side  brasses  A  and  B,  have  their  outer  sides 
inclined  which  abut  against  the  adjustable  wedges  E  and  F. 

To  take  up  wear,  the  side  brasses  are  forced  nearer  together  by  adjusting 
the  bolts  3  and  4,  which  are  attached  to  the  wedges  E  and  F.  The  upper 
brass  C,  may  be  adjusted  by  filing  off  sufficient  metal  at  the  lower  extremities, 
and  tightening  bolts  1  and  2. 


SCREW 
ADJUSTMEWT 


ENGINE 
FRAME 


Fig.  323. — Main  bearing  of  the  Skinner  engine  having  screw  adjustment,  of  the  outer  brass. 


Sometimes  liners  are  inserted  between  the  upper  and  side  brasses,  forming 
an  easy  mode  of  adjustment. 

The  lower  brass  D,  is  raised  for  wear  by  inserting  liners  between  it  and 
the  bearing  box.  In  some  designs  wedge  adjustment  is  provided  for  the 
lower  brass. 

The  side  brasses  are  sometimes  fitted  with  screw  adjustment  in  place  of 
wedges.  On  some  engines,  as  shown  in  fig.  323,  only  one  outer  side  brass  A, 
is  adjustable.  In  this  construction,  the  adjustment  always  being  made  on 
one  side  changes  the  position  of  the  shaft  which  makes  the  cylinder  clear- 
ance unequal,  unless  liners  be  inserted  between  box  and  opposite  brass. 


STEAM  ENGINE  PARTS 


169 


Figs.  324  and  325. — Detail  of  locomotive  driving  journal  box  and  assembly  in  frame.  In  fig. 
324,  A,  is  the  box  proper  which  carries  part  of  the  weight  of  the  engine,  C,  being  the  bearing. 
Underneath  a  receptacle  B.is  filled  with  cotton  waste  which  is  saturated  with  oil  for  lubri- 
cation. B,  is  held  in  position  by  two  pins  P  P',  as  in  fig.  325.  Th.e  box  is  arranged  so  as  to  slide 
up  and  down  in  the  jaws  of  the  frame.  A  spring  S,  is  then  placed  over  the  box  and  above  the 
frame  as  shown,  resting  on  a  W,  shaped  saddle  G,  which  bears  on  the  top  of  the  box.  The  frame 
is  suspended  to  the  end  of  the  spring  by  rods  or  bars  R  R',  called  spring  hangers.  Since  the 
boiler  and  most  of  the  other  parts  are  fastened  to  the  frames,  their  weight  is  suspended  on 
the  ends  of  the  springs,  which  cushion  the  weight  they  bear. 


170 


STEAM  ENGINE  PARTS 


Figs.  324  and  325  show  detail  of  locomotive  journal  box  and 
assembly  in  frame. 

On  stationary  engines,  not  self-contained,  the  second  bearing 
for  the  shaft  is  called  the  outboard  hearing,  and  as  the  stresses 


Fig.  326. — Outboard  bearing  and  pillow  block  of  the  Murray- Corliss  engine.  By  means  of  the 
wedge,  bolts,  and  set  screws  as  shown,  the  position  of  the  bearing  may  be  adj-usted  either 
vertically  or  horizontally.  All  engines  that  are  not  self-contained  should  have  this  type  of 
outboard  bearing  to  secure  precision  in  alignment. 


GAUG 


OILING 
RINGS 


DRAIN 


Figs.  327  and  328. — Self -oiling  bearing.  The  oiling  rings  which  dip  into  the  oil  reservoir  be- 
neath the  bearing,  in  turning  with  the  shaft,  carries  oil  up  to  the  bearing.  A  glass  gauge  at 
the  left  indicates  the  height  of  the  oil  in  the  reservoir. 


STEAM  ENGINE  PARTS 


171 


here  are  less  severe,  simpler  means  of  adjustment  for  the  brasses 
are  provided. 

•  Other  important  adjustments  are  here  necessary.  In  erecting  the  engine, 
it  would  be  difficult  to  get  the  bearing  in  line  if  it  were  attached  direct  to 
the  foundation,  hence  provision  is  made  whereby  the  bearing  may  be  moved 
both  up  and  down,  and  sidewise.  The  bearing  together  with  this  means  of 
adjustment  is  called  a  pillow  block,  the  usual  construction  being  shown  in 
fig.  326.  A  wedge  A,  is  inserted  between  the  base  B,  of  the  bearing  and  the 
base  plate  C.  By  turning  the  screws  D,  and  E,  the  wedge  is  moved  alcn^ 
the  inclined  surface  F  which  raises  or  lowers  the  bearing. 

A  sidewise  adjustment  is  made  by  means  of  the  screws  F  and  C. 


Figs.  329  and  330. — Detail  of  main  bearing  of  a  marine  engine  showing  method  of  fastening 
the  bearing  bolts  on  large  engines. 

In  making  these  adjustments  the  holding  down  bolts  1,  2,  3,  4  are  first 
loosened  and  then  tightened  after  making  the  adjustment.  Two  large 
anchor  bolts  M,  S,  secure  the  pillow  block  to  the  foundation. 

A  projecting  rim  R  extends  around  the  base  plate  which  retains  the 
waste  oil  from  the  bearing.  Usually  a  pipe  is  attached  to  the  base  plate 
to  allow  the  oil  to  drain  a  vessel. 

The  Fly  Wheel. — In  order  to  keep  the  reciprocating  parts 
of  a  steam  engine  in  motion  at  the  dead  centers,  a  large  heavy 
wheel  is  attached  to  the  shaft  which  by  its  momentum^  acts  as 
a  reservoir  of  energy. 

*NOTE. — Momentum  is  the  power  of  overcoming  resistance  possessed  by  a  body  by  reason 
of  its  motion  and  weight.    It  is  that  which  makes  a  moving  body  hard  to  stop. 


172 


STEAM  ENGINE  PARTS 


In  other  words,  the  excess  power  produced  by  the  engine  in 
the  early  part  of  the  stroke  is  stored  up  in  the  fly  wheel,  and 
given  out  by  it  in  the  latter  part  where  little  or  no  power  is 
developed  on  account  of  the  expansion  of  the  steam  and  the 
engine  passing  the  dead  center. 

The  fly  wheel,  therefore,  on  account  of  its  inertiaf,  tends  to 
keep  the  speed  constant  in  spite  of  the  variable  turning  effect 
produced  during  the  stroke. 


Figs.  331  and  332. — Southern  pillow  block  and  pedestal.  The  pillow  block  has  both  vertical 
and  horizontal  adjustments,  whereby  the  engine  shaft  may  be  readily  adjusted  without 
jacking  up  shaft.  The  construction  is  such  that  the  pillow  block  may  be  removed  from  sole 
plate  without  disconnecting  the  latter  from  foundation.  The  journal  is  lined  with  Babbitt 
metal.  The  pedestal  bearing  was  designed  to  meet  the  demand  for  an  outer  bearing  that  would 
add  to  the  appearance  of  engine  and  engine  room,  and  avoid  the  necessity  of  extending 
♦  masonry  of  outer  pier  through  floor  of  engine  room,  which  is  always  more  or  less  objectionable. 
The  base  has  large  bearing  surface,  and  rests  in  same  plane  as  engine.  Wear  is  taken  up  by 
means  of  adjusting  screws  and  quarter  boxes;  the  upper  and  lower  bearings  adjust  them- 
selves automatically  to  the  shaft.  Pedestal  has  oil  catch  basins,  and  approved  method  of 
lubrication. 


tNOTE. — Inertia  is  that  property  of  a  body  on  account  of  which  it  tends  to  continue 
in  the  state  of  rest  or  motion  in  which  it  may  be  placed,  until  acted  upon  by  some  force. 

NOTE. — The  moment  of  inertia  of  the  weight  of  a  body  with  respect  to  an  axis  is  the 
algebraic  sum  of  the  products  of  the  weight  of  each  elementary  particle  by  the  square  of  its  distance 
from  the  axis.  The  moment  of  inertia  varies  in  the  same  body,  according  to  the  position  of 
the  axis.  It  is  the  least  possible  when  the  axis  passes  through  the  center  of  gravity.  To  Mnd 
the  moment  of  inertia  in  a  body,  referred  to  a  given  axis,  divide  the  body  into  small  parts 
of  regular  figure.  Multiply  the  weight  of  each  part  by  the  square  of  the  distance  of  its  center  of 
gravity  from  the  axis.    The  sum  of  the  product  is  the  moment  of  inertia. 


|Hp  In  the  ca^ 


STEAM  ENGINE  PARTS 


173 


k  In  the  case  of  a  single  crank  engine  the  variation  of  the  turning 
"effect  is  large,  while  with  triple  expansion  engines  having  three 
cranks  at  120°,  the  variation  is  reduced  considerably.  It  is 
clear,  therefore,  that  a  large  and  heavy  fly  wheel  is  more  nec- 
essary for  a  single  crank  engine  than  for  one  of  the  same  power 
with  three  cranks. 

The  four  cycle  gas  engine  is  an  example  of  extreme  fly  wheel  require- 
ments. Here  there  is  only  one  impulse  or  power  stroke  in  two  revolutions; 
hence,  the  fly  wheel  must  receive,  during  the  power  stroke,  enough  energy 


Fig.  333.— Various  types  of  Vilter  fly  wheels. 


to  keep  the  engine  moving  at  approximately  uniform  speed  during  the 
three  non-power  strokes  against  the  back  pressure  of  exhaust,  suction  and 
compression.  The  large  fly  wheels  fitted  to  gas  engines  clearly  indicate 
the  variable  and  intermittent  nature  of  the  turning  effect.* 

On  small  engines,  power  is  usually  transmitted  direct  from 
the  fly  wheel,  there  being  no  separate  pulley  for  the  belt. 

The  diameter  of  the  fly  wheel  is  governed  by  conditions  of 


*NOTE. — So  far  as  turning  effect,  that  is,  the  number  of  impulses  per  revolution,  is 
concerned,  one  double  acting  steam  cylinder  is  equivalent  to  two  gas  engine  cylinders  of  the 
two  cycle  type,  or  four,  of  the  four  cycle  type. 


174 


STEAM  ENGINE  PARTS 


service,  and  limited  by  the  tangential  velocity,  that  is,  by  the 
speed  at  the  rim,  or  its  equivalent,  the  belt  speed. 

Owing  to  the  centrifugal  force"^  which  increases  with  the  speed 
and  which  tends  to  burst  the  wheel,  it  is  not  advisable  to  run 
fly  wheels  at  a  rim  speed  higher  than  6,000  feet  per  minute,  or 
roughly,  a  mile  a  minute,  f 


Figs.  334  and  335. — Harris- Corliss  ordinary  split  belt  wheel.  Wheels  of  9  feet  and  less 
diameter  are  made  whole,  and  those  from  10  ft.  to  17  ft.,  are  made  in  halves  fastened  by- 
turned  bolts  driven  into  reamed  holes.  Each  half  is  provided  with  four  oval  arms,  a  center 
rib,  increasing  in  depth  toward  the  arm,  and  a  return  flange  follows  the  outer  edge  of  the 
wheel  on  both  sides.  All  wheels  above  14  ft.  diameter,  made  in  halves,  have  the  rim  joints 
made  through  the  central  arms,  instead  of  between  arms. 


Example, — How  large  a  fly  wheel  could  be  safely  used  on  an  engine 
making  200  revolutions  per  minute? 


*NOTE. — This  is  the  force  which  acts  on  a  body  revolving  in  a  circular  path,  tending  to 
force  it  farther  from  the  center  of  the  circle,  because  all  moving  bodies  move  in  straight  lines 
when  not  acted  upon  by  external  forces. 

fNOTE. — For  any  given  material,  as  cast  iron,  the  strength  to  resist  centrifugal  force 
depends  only  on  the  velocity  of  the  rim,  and  not  upon  its  bulk  or  weight.  Chas.  T.  Porter 
states  that  no  case  of  the  bursting  of  a  fly  wheel  with  a  solid  rim  in  a  high  speed  engine  is  known. 
He  attributes  the  bursting  of  wheels  built  in  segments  to  insufficient  strength  of  the  flanges 
and  bolts  by  which  the  segments  are  held  together. 


STEAM  ENGINE  PARTS' 


175 


Taking  6,000  feet  per  minute  as  the  limit  of  rim  speed,  the  distance 
traveled  per  revolution  by  a  point  on  the  rim,  or  the  circumference  of  the 
wheel  is : 

6,0004-200  =  30  feet, 
.from  which,  the  diameter  corresponding  is: 

30-f-7r*=9.5  feet  (approximately). 

It  is  important  that  an  engineer  should  be  able  to  determine 
the  size  of  belt  required  to  transmit  a  given  horse  power.    There 


Figs.  336  and  337. — Harris-Corliss  segmental  belt  wheel  as  used  on  large  engines.  Wheels 
18  feet  and  upward  in  diameter  are  constructed  in  segments,  having  8,  10  or  12  segments 
in  each  wheel,  and  the  same  number  of  arms.  The  latter  are  of  oval  hollow  construction, 
as  shown  in  the  section  A  A,  this  being  the  form  which  gives  maximum  strength.  The  flanges 
are  planed  to  a  fit.  The  arms  are  bolted  to  the  rim  segments  and  are  held  at  the  shaft  be- 
tween the  hub  flanges. 


are  any  number  of  rules  for  belt  sizes,' and  the  results  obtained 
by  their  application  are  quite  varied.  The  following  rule  which 
is  easily  remembered,  will  be  found  suitable  for  all  ordinary  cases; 


*NOTE. — TT  (pronounced  pi)  is  a  greek  letter  used  to  denote  the  ratio  between  the  diameter 
and  circumference  of  a  circle.  Its  value  is  3.1416  (nearly);  that  is,  the  circumference  of  a 
circle  is  equal  to  3.1416  multiplied  by  the  diameter. 


176 


STEAM  ENGINE  PARTS 


it  gives  a  belt  width  amply  large  to  deliver  the  power  without 
undue  strain  or  wear. 


Rule. — A  single  belt  one  inch  wide,  traveling  1,000  feet  per 
minute  will  transmit  one  indicated  horse  power. "^  A  double  belt 
will  transmit  twice  this  amount. 

Example. — What  size  double  belt  would  be  required  for  a  11"  X  24" 
Corliss  Engine  with  an  8  foot  fband  fly  wheel,  running  at  110  revolutions 
per  minute  and  developing  60  indicated  horse  power? 


Figs.  338  and  339.— Large  fly  wheel  for  Corliss  engine.  In  this  wheel,  which  is  28  ft.  in  diameter, 
the  rim  is  made  in  segments  and  joined  by  heavy  I  links.  The  hub  is  in  halves,  and  between 
the  flanges  of  these  halves,  the  inner  ends  of  the  arms  are  bolted.  The  unit  division  of  the 
body  of  the  wheel  is  one  arm  with  its  segment.  The  rim  center  is  reinforced  by  side  plates 
of  cast  steel,  each  of  which  covers  the  angle  of  two  arm  spaces,  and  they  break  joint  on  the 
two  sides  so  that  there  is  nowhere  more  than  one  link  joint  at  any  cross  section  of  the  rim. 
The  whole  rim  is  strongly  fastened  together  by  stout  pins,  which  are  forced  into  reamed 
holes  by  hydraulic  pressure,  then  riveted  cold. 


*NOTE. — This  corresponds  to  a  working  strain  of  33  pounds  per  inch  of  width.  Some 
authorities  give  for  single  belts  in  good  condition  a  working  tension  of  45  pounds  per  inch  of 
width,  and  64  pounds  for  a  double  belt. 

fNOTE. — The  term  "band  fly  wheel"  means  that  the  wheel  has  a  wide  rim  for  the  belt 
so  that  no  pulley  is  required.  When  a  pulley  is  used,  the  rim  is  made  narrow  and  thick  so 
that  the  wheel  will  not  take  up  much  room  in  the  direction  of  the  shaft. 


STEAM  ENGINE  PARTS 


177 


Fig.  340. — Providence  bal- 
ance fly  wheel  made  in 
halves,  principally  used 
on  engines  directly  con- 
nected to  electric  genera- 
tors, to  a  line  of  shafting, 
or  in  any  service  where 
belts  or  ropes  are  not  used 
to  transmit  the  power 
from  the  engine. 


Fig.   341.~Providence  pul- 

.    ley  wheel  made  in  halves. 

The  rim  joint  is  made  at 

a  point  midway  between 

the  arms  as  shown. 


L78 


STEAM  ENGINE  PARTS 


The  rim  speed  per  minute  of  the  fly  wheel  is : 

Diameter  X      tt      X  rev.  per  min.  \  _  /  f t.  per  min. 
8        X3.1416X  110         /  ~  \  2,765  feet. 

Since  a  single  belt,  traveling  at  1,000  feet  per  minute,  transmits  one  horse 
power  per  inch  of  width  it  will  when  run  2,765  feet  per  minute  transmit: 

2,765^1,000  =  2.765  horse  power. 


Figs.  342. — Turning  a  large  Vilter  rope  wheel 


A  double  belt  will  transmit  twice  this  amount  or 

2.765X2=5.53  horse  power. 

Hence,  the  width  of  a  double  belt  for  60  horse  power  is 

60 -f-5.53  =  11  inches. 

The  fly  wheel  rim  should  be  somewhat  wider  than  the  belt,  so  as  to  lea^ 
a  margin  of  34  to  3^  inch  on  each  side.    This  prevents  the  belt  over  running 
the  rim  by  any  sidewise  movement  due  to  uneven  working. 


THE  SLIDE  VALVE  179 


CHAPTER  4 
THE   SLIDE  VALVE 


Oues.    What  is  a  slide  valve?* 

Ans.  A  slide  valve  is  a  long  rectangular  boxlike  casting 
designed  to  secure  the  proper  distribution  of  steam  to  and  from 
the  cylinder. 

Its  general  form  is  shown  in  fig.  343.  Here  a  portion  of  the  valve  is 
cut  away  exposing  to  view  the  exhaust  edge  of  the  valve,  the  exhaust  port, 
bridges,  and  one  of  the  steam  ports. 

Oues.     What  other  name  is  given  to  the  slide  valve? 

Ans.  It  is  sometimes  called  the  simple  D  valve],  on  account 
of  its  resemblance  to  the  capital  letter  D  turned  with  the  fiat 
side  down,  and  having  that  side  practically  all  removed,  as  shown 
in  the  black  cutaway  section  in  fig.  343. 

Oues.  What  are  the  requirements  of  a  slide  valve  with 
respect  to  the  distribution  of  the  steam? 

Ans.  Considering  first  only  one  end  of  the  cylinder,  it  must: 
1,  admit  steam  to  the  cylinder  just  before  the  beginning  of  the 


*NOTE. — In  its  broad  sense  the  term  "slide  valve"  includes  all  sliding  valves,  as  dis- 
tinguished from  rotary  valves. 

fNOTE. — The  slide  valve  in  its  crude  form  was  invented  by  Matthew  Murray  of  Leeds, 
England,  toward  the  end  of  the  eighteenth  century.  It  was  improved  upon  by  James  Watt, 
but  the  simple  D  slide  valve  in  use  today,  is  credited  to  Murdock,  an  assistant  of  Watt.  It 
came  into  general  use  with  the  introduction  of  the  locomotive,  although  Oliver  Eames,  of 
Philadelphia,  appears  to  have  realized  its  value,  in  fact,  for  years  before  the  advent  of  the 
locomotive  he  applied  it  to  engines  of  his  own  make. 


180 


THE  SLIDE  VALVE 


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THE  SLIDE  VALVE 


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182 


THE  SLIDE  VALVE 


As  shown  in  fig.  344,  the  seat  extends  from  A  to  H.  B,  C,  and  F,  G,  are 
the  steam  ports,  and  D,  E,  the  exhaust  port.  The  steam  ports  are  separated 
from  the  exhaust  port  by  two  walls  C,  D,  and  E,  F,  called  bridges. 

In  some  engines  there  are  finished  vertical  guide  surfaces  along  the 
two  sides  of  the  seat  to  prevent  any  side  motion  of  the  valve.  The  port 
edges  are  terminated  by  small  fillets  as  at  M  and  S,  so  that  they  may  be 
properly  machined. 

Oues.     What  is  the  steam  edge  of  a  valve? 

-  STEAM  EDGES  OF  VALVE    - 
EXHAUST  EDGES  OF  VALVE 


-EXHAUST  EDGES  OF  STEAM  PORTS- 
5TEAM  EDGES  OF  5TtAM  PORTS- 

Fig.  345. — Sectional  view  of  valve  on  seat  illustrating  the  term  steam  edge,  exhaust  edge  of 
both  valve  and  seat. 

Ans.  The  edge  which  opens  or  closes  the  port  admitting 
and  cutting  off  the  steam  supply  to  the  cylinder. 

Oues.    What  is  the  exhaust  edge  of  a  valve? 

Ans.  The  edge  which  opens  or  closes  the  port  for  release  or 
compression. 

Owes.  What  is  the  difference  between  a  port  and  a 
passage? 

Ans.-  A  port  is  the  entrance  at  the  valve  seat  to  1,  either 
steam  passage  leading  to  the  cylinder,  or  2,  the  exhaust  passage 
leading  to  the  exhaust  pipe. 


THE  SLIDE  VALVE 


183 


Owes.  What  governs 
the  length  (A  H,  fig.  344) 
of  the  valve  seat? 

Ans.  It  should  be  less 
than  the  length  of  the 
valve  plus  its  travel  so  that 
the  valve  will  over  travel  to 
avoid  wearing  shoulders  in 
the  seat.  ^i^Mk^-^'  ' 


In  the  case  of  unbalanced 
valves  the  valve  seat  should 
be  as  short  as  possible  to 
reduce  the  unbalancing  by 
over  travel  as  shown  in  fig. 
347. 


Oues.  Why  is  the 
length  of  the  ports 
made  much  greater 
than  the  width? 

Ans.  To  secure  the  re- 
quired amount  of  port 
opening  with  very  little 
valve  movement,  and  that 
the  ports  may  be  quickl3^ 
opened  and  closed  to  re- 
duce wire  drawing. 

Ones.  What  is  wire 
drawing? 

Ans.  The  effect  pro- 
duced   by    steam    flowing 


184 


THE  SLIDE  VALVE 


through  a  constricted 
passage,  which  results 
in  a  fall  of  pressure  with 
its  attendant  loss  in 
engine  operation. 

Ones.  What  gov- 
erns the  length  of  the 
ports  ? 

Ans.  The  diameter 
of  the  cylinder;  they 
are  usually  made  about 
.8  of  this  diameter. 

Ones.  What  gov- 
erns the  width  of  the 
ports? 

Ans.  For  a  given 
port  length,  the  width 
depends  on  the  amount 
of  area  required  for  th^ 
proper  flow  of  the  steam. 

Oues.  Why  is  the 
exhaust  port  made 
wider  than  the  steam 
ports? 

Ans.     Because  the  valve,   on  account  of  the  extent  of  its 
movement,  partly  covers  this  port  during  exhaust. 

In  fig.  346,  the  valve  is  shown  at  the  extreme  point  of  its  travel,  in  which 
position  the  exhaust  port  H  H'  is  covered  by  the  valve  a  distance  H  C, 
leaving  only  the  opening  C  H',  through  which  exhaust  steam  may  escape. 


Figs.  348  and  349. — Two  views  of  Brownell  high 
speed  engine  cylinder,  showing  valve  seat  and 
entrance  of  one  of  the  steam  passages  at  the  end 
of  the  cylinder;  also  arrangement  of  the  studs, 
and  exhaust  outlet. 


THE  SLIDE  VALVE  185 


In  a  well  designed  valve  this  opening  should  not  be  less  than  the  width  F  G, 
of  the  steam  port.  When  the  exhaust  opening  H'C,  is  less  than  the  width 
of  the  steam  port,  the  exhaust  is  said  to  be  choked  by  the  valve. 


Oues.     How  is  the  size  of  the  steam  port  obtained? 

Ans.     From  the  area  and  speed  of  the  piston,  and  an  assigned 
velocity  of  6,000  feet  per  minute.* 

Owes.     What  names  are  given  to  the  principal  parts 
of  a  slide  valve? 


Figs.  350  to  353. — Brownell  balanced  slide  valve  and  pressure  plate  for  the  cylinder  shown  in 
figs.  348  and  349.  The  valve  is  a  single  casting  working  between  its  seat  and  the  pressure 
plate.    It  is  double  ported  and  is  provided  with  means  for  relief  from  water. 


Ans.  The  edge  at  either  end  of  the  valve  is  called  the  steam 
edge  as  shown  in  fig.  345,  because  this  edge  controls  the 
admission  of  steam  to  the  cylinder,  and  for  a  similar  reason 
each  inner  edge  is  called  the  exhaust  edge.f 


*NOTE. — In  engines  having  separate  exhaust  ports,  the  steam  ports  are  proportioned 
for  a  velocity  of  8,000  feet  per  minute,  but  when  the  sarne  port  is  used  for  both  admission 
and  exhaust,  the  port  must  evidently  be  proportioned  with  respect  to  the  exhaust,  that  is 
the  steam  should  be  exhausted  at  less  velocity  than  the  velocity  of  admission.  In  the  exhaust 
pipe  the  velocity  should  be  still  less  thah  in  the  steam  passage — usually  4,000  feet  per  minute. 

f  NOTE. — These  terms  should  be  remembered  as  well  as  the  similar  names  given  to  the 
edges  of  the  steam  ports  as  shown  in  fig.  345. 


186 


THE  SLIDE  VALVE 


The  area  of  the  steam  port  is  found  as  follows : 

area  piston  in  sq.  ins.  X  piston  speed  in  ft. 


Area  steam  port 


6,000 


Owes.  What  important  defect  is  there  in  the  operation 
of  the  ordinary  slide  valve? 

Ans.  The  excessive  pressure  caused  by  the  steam  pressing 
the  valve  against  its  seat  causing  considerable  friction  and 
wear.  * 


-FACE 


FACE- 


Fig.  354. — Sectional  view  of  slide  valve  showing  the  principal  parts.     It  is  important  to 
remember  the  names  given  in  the  figure. 

Example. — What  will  be  the  force  required  to  move  a  9  X  18  slide  valve, 
if  there  be  on  it  an  unbalanced  steam  pressure  of  140  pounds  per  square 
inch,  and  the  resistance  due  to  friction  be  .02  of  the  total  load  on  the  valve? 


*NOTE. — A  slide  valve  whose  outside  dimensions  are,  say,  9X18  inches  has  an  area  of 
162  square  inches.  If  a  boiler  pressure  of  140  pounds  per  square  inch  be  exerted  on  this  area, 
then  the  total  pressure  on  the  area  is  162X140=22,680  pounds.  The  actual  pressure  which 
tends  to  force  the  valve  against  its  seat  is  variable,  as  during  some  portions  of  the  stroke  the 
steam  in  the  ports  under  the  valve  exerts  an  upward  pressure,  which  opposes  that  on  top. 
The  pressure  on  top  is  also  influenced  by  the  fit  of  the  valve.  If  it  be  not  steam  tight,  more 
or  less  steam  will  get  between  the  valve  and  its  seat,  and  thus  act  against  the  pressure  on  top, 
whereas  if  the  valve  be  steam  tight,  no  such  action  will  occur.  In  any  event  the  pressure  on 
top  of  an  unbalanced  valve  is  very  considerable. 


THE  SLIDE  VALVE 


187 


Area  of  valve  =9X18  =  162  sq.  ins. 
Total  load  on  valve  due  to  steam  pressure : 
=  162X140  =  22,680 
Force  required  to  move  the  valve: 

=  22,680 X. 02  =  453.6  pounds 


Fig.  355. — Cylinder  of  Houston,  Stanwood  and  Gamble  automatic  engine  with  valve  chest 
cover  removed  showing  balanced  slide  valve.    Fig.  356  shows  a  sectional  view  of  this  valve. 

Qvies.  What  provision  is  sometimes  made  for  relieving 
the  pressure  on  the  slide  valve? 

Ans.  Various  devices  have  been  used  to  exclude  sfeam  from 
the  top  of  the  valve,  so  that  the  pressure  cannot  be  exerted 
in  a  direction  which  would  press  the  valve  against  its  seat.*  The 
valve  is  then  said  to  be  balanced. 


•NOTE. — Experiments  with  small  engines  show  that  from  one  to  two  per  cent  of  the 
whole  power  of  the  engine  is  absorbed  in  moving  the  slide  valve  when  unbalanced. 


188 


THE  SLIDE  VALVE 


Lap 


Oues.     What  is  the  lap  of  a  valve? 

Ans.     It  is  that  portion  of  the  valve  face  which  overlaps  the 
steam  ports  when  the  valve  is  in  its  central  position. 


ENI.ARai» 


Fig.  356. — Sectional  view  of  Houston  Stanwood  and  Gamble  balanced  slide  valve.  It  is  held 
against  the  seat  by  steam  pressure  on  a  small  area  of  the  back  of  the  valve  and  by  this 
means  is  made  nearly  steam  tight.  Also,  the  valve  by  this  means  is  made  to  automatically 
follow  up  its  wear,  so  that  the  steam  consumption  will  be  lower  after  the  engine  has  been 
in  use  for  a  time,  rather  than  higher. 

In  fig.  357  AB,  is  the  outside  or  steam  lap,   and  CD,  the  inside  or 
exhaust  lap.  f 

^^   EXHAUST     ^ 


Fig.  357. — The  plain  D  slide  valve  showing  "lap."    A  B  is  the  outside  or  steam  lap;   C  D  ,  the 
inside  or  exhaust  lap.    The  figure  also  illustrates  the  neutral  position  of  the  valve. 


fNOTE. — Since,  in  some  types  or  engine,  steam  is  admitted  at  the  inside  edges  of  the 
ports  and  exhausted  at  the  outside  edges,  the  terms  steam  lap  and  exhaust  lap  are  therefore 
sometimes  used  to  avoid  confusion. 


THE  SLIDE  VALVE 


189 


Oues.     What  is  usually  understood  by  the  term  lap? 

Ans.     The  outside  or  steam  lap. 

Oiies.     What  is  the  effect  of  lap? 

Ans.  It  causes  the  valve  to  shut  off  the  supply  of  live  steam 
to  the  cylinder  before  the  end  of  the  stroke,  the  greater  the 
amount  of  lap  the  sooner  does  this  occur. 

Ques.     What  is  the  effect  of  inside  lap? 

M 

I 
NEUTRAL    POSITION    OF  VALVE 


NEGATIVE     INSIUE  LAP 


POSITIVE    INSIDE   LAP 


Fig.  358. — Illustrating  negative  and  positive  inside  lap.  A  valve'is  sometimes  given  negative 
inside  lap  at  one  end  to  equalize  release  and  compression;  the  irregularity  being  due  to  the 
angularity  of  the  connecting  rod. 


Ans.  It  causes  the  valve  to  open  later  for  exhaust  and  close 
sooner,  thus  shutting  in  a  larger  portion  of  the  exhaust  steam. 

Oues.     What  is  the  neutral  position  of  a  valve? 

Ans.  Its  central  position,  or  the  mid-point  of  its  travel  as 
shown  in  fig.  358,  overlapping,  equally  the  steam  ports.  In 
this  position  a  line  drawn  through  the  center  of  the  valve  will 


190 


THE  SLIDE  VALVE 


coincide  with  a  line  drawn  through  the  center  of  the  exhaust 
port,  when  the  exhaust  lap  is  the  same  at  each  end.* 

Oues.     What  is  negative  inside  lap? 

Ans.  The  space  (as  A  B,  fig.  358)  sometimes  left  at  one  end 
of  the  valve  between  its  exhaust  edge,  and  the  exhaust  edge 
of  the  steam  port  when  the  valve  is  in  its  neutral  position. 

It  is  sometimes,  though  ill  advisedly,  called  inside  clearance.    The  differ- 
ence between  negative  and  positive  \  inside  lap  is  indicated  in  the  figuie. 


Fig.  359. — Illustrating  "line  and  line"  position. 


Oues.     Why  is  a  valve  sometimes  given  negative  inside 
lap  at  one  end? 

Ans.     To  equalize  certain  irregularities  of  exhaust  due  to  the 
angularity  X  of  the  connecting  rod. 


*NOTE. — These  center  lines  are  convenient  in  locating  the  valve  for  different  positions. 

tNOTE. — The  term  inside  lap  unqualified  always  means  positive  inside  lap. 

JNOTE. — The  term  angularity  and  its  effect  on  the  action  of  the  valve  gear  is  later  fully 
explained. 


THE  SLIDE  VALVE 


191 


f 


Oues.     What  is  the  effect  of  negative  inside  lap? 

Ans.     It  causes  the  valve  to  open  sooner  and  close  later  to 
;haust. 

That  is,  pre-release  begins  earlier,  and  compression  later. 


Oues.     What  is  *'line  and  line"  position? 

Ans.     When  one  edge  of  the  valve  is  in  the  same  line  or 
plane  with  the  corresponding  edge  of  the  port  as  in  fig.  359. 

i  extra  wearing  surface 

I^wAO^s^^-^vO^    outside  admission 


Fig.  360. — Sectional  view  of  Phoenix  cylinder  showing  double  disc  piston  valve.  The  valve 
admits  steam  from  the  ends,  the  valve  casing  being  surrounded  by  live  steam.  The  two  inner 
discs  provide  extra  wearing  surface. 


Here  the  steam  edge  of  the  valve  is  in  line  with  the  steam  edge  of  the 
port,  and  valve  is  at  the  point  of  opening  the  port. 

Lead 

Oues.     What  is  lead  ? 

Ans.     The  amount  by  which  the  port  is  open  for  the  adraission 


192 


THE  SLIDE  VALVE 


of  steam  when  the  piston  is  at  the  beginning  of  the  stroke.'" 

For  instance,  in  fig.  361,  the  port  is  open  a  distance  A  A',  which  is  the 
lead.  This  is  outside  lead  as  distinguished  from  inside  lead.  It  is  ^  also 
called  positive  lead  to  distinguish  it  from  negative  lead. 


Oues.     What  is  negative  lead? 

Ans.     The  amount  by  which  the  steam  port   is   closed   to 
admission  when  the  piston  is  at  the  beginning  of  the  stroke. 


Fig.  361. — Valve  in  lead  position 
beginning  of  the  stroke. 


This  is  the  position  of  the  valve  when  the  piston  is  at  1 


Owes.     What  is  the  object  of  lead? 

Ans.  Lead  is  given  to  a  valve  in  order  to  admit  live  steam 
to  the  cylinder  before  the  beginning  of  the  stroke  so  that  the 
pressure    of   the    compressed    exhaust    steam   in    the    clearance 


*NOTE. — Lead  varies  with  the  size  and  type  of  engine  usually  from  zero  to  about  % 
of  an  inch.  Small  or  medium  sized  slow  speed  engines  may  have  from  V64  to  Vis,  medium 
speed  engines  a  greater  amount,  and  in  the  case  of  high  speed  engines  still  more  unless  there  be 
considerable  compression.  Vertical  engines  usually  have  more  lead  at  the  lower  cylinder  end 
than  at  the  upper,  in  order  to  assist  the  compression  in  resisting  the  excess  momentum  at 
the  lower  end  due  to  the  weight  of  the  moving  parts  acting  in  that  direction.  In  general,  the 
greater  the  compression,  the  less  the  amount  of  lead  required.  The  principal  object  of  lead 
is  to  secure  full  steam  pressure  in  the  cylinder  at  the  beginning  of  the  stroke,  rather  than  to 
resist  the  momentum  of  the  moving  parts,  although  in  high  speed  engines  where  the  com- 
pression is  not  sufficient  to  bring  the  moving  parts  to  a  state  of  rest,  an  extra  amount  of  lead 
's  necessary  on  this  account. 


THE  SLIDE  VALVE 


193 


space  will  be  increased  to  boiler  pressure  at  the  beginning  of 
the  stroke.  This  enables  the  piston  to  begin  its  stroke  with 
the  maximum  pressure. 

Oi^es.     What  is  the  object  of  negative  lead? 

Ans.  On  some  types  of  valve  gear,  as  the  link  motion,  the 
lead  increases  with  the  degree  of  expansion.  Hence,  in  full 
gear,  that  is,  for  the  maximum  cut  off,  a  negative  lead  is  given 
to  prevent  excessive  positive  lead  when  cutting  off  very  early. 


Fig.  362. — ^Valve  in  negative  lead  position.    Negative  lead  is  sometimes  given  with  link  motion 
full  gear  to  prevent  excessive  lead  when  cutting  off  short,  as  on  locomotives. 

With  negative  lead,  the  valve  does  not  open  for  the  admission  of  steam 
until  after  the  beginning  of  the  stroke. 


Owes.     What  is  inside  or  exhaust  lead? 

Ans.     It  is  the  amount  by  which  the  steam  port  is  opened  to 
exhaust  when  the  piston  is  at  the  beginning  of  the  stroke. 

Oues.     What  is  constant  lead? 

Ans.     Lead   which  does  not   change  for  different   degrees   of 
expansion. 


NOTE, — Negative  lead  is  sometimes  given  to  the  valves  of  express  locomotives  when 
fitted  with  link  motion  valve  gear.  Since  the  action  of  the  link  increases  the  lead  for  an  early 
cut  off  (the  cut  off  used  except  at  starting)  negative  lead  is  given  for  full  cear  so  that  the  lead 
will  not  be  excessive  at  early  cut  off. 


194 


THE  SLIDE  VALVE 


Owes.  What  is 
variable  lead  ? 

Ans.  Lead  which 
changes  with  the 
degree  of  expan- 
sion. 

Oues.  What  is 
equal  lead  ? 

Ans.  Lead  which 
is  the  same  at  each 
end  of  the  cyHnder. 


Figs.  363  and  364.- 


■Valve  in  lead  position  illustrating  variable  MTG'CLdtTtlSSlOTX 
lead;  thus  lead  M,  with  gear  in  late  cut  off  position  is  less  than 
lead  S,  for  early  cut  off.   A  peculiarity  of  the  link  motion  gear  is 

this  variable  lead.    With  the  link  motion  in  shortening  the  cut  OueS       ^^hat  IS 

off  by  "hooking  up";  open  rods  give  increasing  lead,  while  ^           •         t      «.       o 

crossed  rods  give  decreasing  lead.  Dre-adHlissiOIl  ^ 

Ans.  The  flow  of 
live  steam  into 
the  cyHnder  hejore 
the  beginning  of 
the  stroke. 

Oues.  On  what 
does  pre-admis- 
sion depend? 

Ans.  On  the 
amount     of     lead. 

That  is,  the  great- 
er the  lead,  the  soon- 
er   does    the    valve 

„  ,   „^^     xr .  .  open  to  admit  steam 

Figs.   365   and   366. — Valve  in  lead  positions  illustrating  equal  K^fr^r^  +Vi^  Kom'r.r.in  -r 

lead,  that  is,  lead  M  at  one  end  of  the  cylinder  is  the  same  as  Deiore  tne  Oeginnmg 

lead  S  at  the  other  end.  of  the  stroke. 


I 


THE  SLIDE  VALVE 


195 


Ques.     What  is  the  object  of  pre-admission? 

Ans  Principally  to  secure  the  full  steam  pressure  at  the 
beginning  of  the  stroke,  and  in  addition,  in  some  cases,  to  assist 
the  compression  in  bringing  the  moving  parts  to  a  state  of  rest. 

Ques.     What  objection  is  there  to  pre-admission? 

Ans.  It  increases  the  period  during  which  live  steam,  at  a 
high  temperature,  is  exposed  to  the  comparatively  cool  cylinder 
walls,  thus  tending  to  increase  initial  condensation. 


Fig.  367. — Valve  fully  opened  for  admission;  this  comes  when  the  piston  is  about  half  way 
between  the  beginning  of  the  stroke  and  cut  off  position.  Usually  the  port  is  only  partially 
opened,  as  here  shown,  because  the  speed  of  the  steam  through  the  port  during  admission 
should  be  greater  than  during  exhaust. 

NOTE. — In  the  design  of  a  steam  engine  it  is  important  to  give  the  proper  amount  of 
port  opening,  for  if  it  be  too  small,  the  velocity  of  the  entering  steam  is  unduly  increased,  re- 
sulting in  a  loss  of  pressure  commonly  known  as  wire  drawing.  On  fixed  cut  o/f  engines,  the 
port  opening  may  be  less  than  the  port  because  the  latter  is  proportioned  to  give  the  proper 
velocity  of  the  exhaust  steam.  With  variable  cut  off  gears,  whose  action  reduces  the  port 
opening  in  shortening  the  cut  off,  as  for  instance  the  link  motion,  it  is  usual  to  provide  excess 
port  opening  at  full  gear  in  order  to  obtain  adequate  admission  when  linked  up.  For  instance 
on  locomotives  which  operate  normally  at  short  cut  off,  the  port  opening  in  full  gear  is  con- 
siderable, even  exceeding  the  width  of  the  port  as  in  fig.  375. 

NOTE. — Engines  are  commonly  designed  with  ports  and  passages  proportioned  for  a 
nominal  steam  speed  of  6,000  to  8,000  feet  per  minute  when  cutting  off  at  about  60%  of  the 
stroke,  using,  instead  of  the  maximum  velocity,  the  average  velocity,  that  is 

area  piston  X  piston  speed 
area  ■t>ort  = 

the  port  and  piston  areas  being  taken  in  sq.  ins.,  and  the  piston  speed  in  feet  per  minute. 

NOTE. — It  must  be  obvious  that  in  determining  the  port  opening,  the  cut  off  should  be 
taken  into  consideration,  since  the  movement  of  the  piston  is  not  uniform  but  starts  from  zero 
at  the  beginning  of  the  stroke  and  gradually  accelerates  to  maximum  velocity  near  mid  stroke, 
then  decreases  to  zero  at  the  end  of  the  stroke.  Prof.  Fessenden  in  his  excellent  book  on  valve 
gears  has  given  an  elaborate  treatment  of  this  subject  which  should  interest  those  engaged  in 
engine  design.  . 


196 


THE  SLIDE  VALVE 


Oues.    What  is  meant  by  initial  condensation? 

Ans.     The  condensation  of  live  steam  in  the  cyHnder  which 
takes  place  during  the  periods  of  pre-admission  and  admission. 

Admission 

Ques.    What  is  admission? 


Kl-^-W 


LEARANCL 


STROKE 


I 


!     I 


t-ZZl 


[-^-APPARENT  CUT  OFF— >{ 

h — — c 


-  REAL  CUT  OFF- 


•l+C 


SCALE 


1        0         \        Z        3       4 

Fig.  368. — The  apparent  and  real  cut  off.  The  effect  of  cylinder  clearance  is  to  make  the 
number  of  expansions  less  than  would  correspond  to  the  apparent  cut  off,  that  is,  the  cut 
off  of  the  valve  gear.  Thus,  .if  the  valve  gear  cut  off  at  one-half  stroke,  there  would  be 
without  clearance,  two  expansions.  With,  say  10  per  cent  clearance,  the  expansions  would 
be  reduced  to  1 -^(.l-^-.5)  =1.66.  The  real  cut  off  would  then  be  1^1.66  =  . 6  stroke. 
In  the  figure  the  clearance  volume  I  includes  besides  the  volume  between  the  piston  at  end 
of  stroke  and  cylinder  head,  the  volume  of  the  steam  passage  (not  shown)  up  to  the  steam  port. 


Ans.     The  flow  of  live  steam'^  into  the  cylinder  from  the 
beginning  of  the  stroke  to  the  point  of  cut  off. 


*N0TE. — Live  steam  is  steam  taken  direct  from  the  boiler,  and  which  has  not  been 
expanded  in  the  cylinder,  as  distinguished  from  steam  which  has  been  admitted  to  the  cylinder 
and  expanded  in  doing  work  on  the  piston. 


THE  SLIDE  VALVE 


197 


Cut  off 

Owes.     What  is  cut  oflf? 

Ans.  It  is  the  closure  of  the 
steam  port  to  the  admission  of 
steam. 


Ones, 
pressed  ? 


How  is  it  usually  ex- 


Ans.  As  a  fraction  of  the  stroke, 
as  one-half,  five-eighths,  or  three- 
fourths  cut  off. 

Oues.  What  is  cut  off  thus 
expressed  called? 

Ans.     The  apparent  cut  off. 

Oues.    Why? 

Ans.  Because  it  does  not  rep- 
resent the  actual  point  at  which 
cut  off  takes  place  when  clearance 
is  considered. 


As  distinguished  from  the  apparent 
cut  off,  the  term  actual  or  real  cut  off  is 
used  to  indicate  the  point  at  which  the 
steam  port  is  closed,  taking  clearance 
into  account. 


Oues. 
off? 


What  is  the  real  cut 


198 


THE  SLIDE  VALVE 


Ans.     The  sum  of  the  apparent  cut  off  plus  the  percentage  of 
clearance. 

For  instance,  if  the  apparent  cut  off  be  one-half,  or  50  per  cent  and  the 
clearance  be  10  per  cent,  then  the  real  cut  off  is  10+50  =  60  per  cent  of  the 
stroke. 

In  fig.  368,  let  the  volume  /,  at  the  end  of  the  cylinder  represent  the 
clearance  in  proportion  to  the  volume  displaced  by  the  piston  during  the 
stroke  L.  This  clearance*  volume  includes  all  the  space  between  the 
piston  when  it  is  at  the  beginning  of  the  stroke  and  the  face  of  the  valve* 
plus  the  volume  of  the  steam  passage  up  to  the  steam  port. 


pre-release: 


Fig.  371. — Position  of  valve  at  beginning  of  pre-release.  This  occurs  just  before  the  piston 
reaches  the  end  of  the  stroke  so  as  to  rid  the  cyHnder  of  most  of  the  steam  before  the  be- 
ginning of  the  return  stroke,  and  thus  reduce  the  back  pressure  of  exhaust  as  much  as  possible. 

It  is  evident  from  the  figure  that  the  distance  the  piston  has  moved  from 
the  beginning  of  the  stroke  does  not  represent  the  real  cut  off,  and  that 
the  latter  is  made  up  of  the  volume  displaced  by  the  piston  plus  the  clearance 
volume,  or  /+C.  Thus  in  the  figure  if  cut  off  occur  when  the  piston  is  at 
5,  as  shown,  the  apparent  cut  off  C,  is  five-tenths  or  one-half  stroke.  The 
actual  cut  off  /+C,  is  six-tenths  stroke. 


Pre-release 


Oues.     What  is  pre-release? 


*NOTE. — The  term  clearance  is  sometimes  used  to  denote  the  linear  distance  between 
the  piston  and  the  cylinder  head  when  the  piston  is  at  the  beginning  of  the  stroke. 


THE  SLIDE  VALVE 


199 


Ans.  The  opening  of 
the  steam  port  to  ex- 
haust before  the  piston 
has  completed  its  stroke, 
as  shown  in  fig.  371. 

If  the  steam  were  con- 
fined in  the  cylinder  until 
the  piston  had  reached  the 
end  of  its  stroke,  there 
would  not  be  time  for  it 
to  escape  without  creating 
considerable  backpressure. 

Oues.  On  what 
does  pre-release  de- 
pend? 

Ans.  Primarily  upon 
the  amount  of  exhaust 
lap,  and  in  design,  upon 
the  conditions  of  oper- 
ation. 

The  proper  amount  of 
pre-release  depends  on  the 
piston  speed,  and  the 
quantity  of  steam  to  be 
discharged.  Usually  the 
valve  is  so  proportioned 
that  pre-release  begins 
about  90  per  cent,  of  the 
stroke. 

Release 

Oues.  What  is  re- 
lease? 

Ans.  The  exhaust  of 
steam  from  the  beginning 
of  the  return  stroke  to 
the  point  of  compression. 


200 


THE  SLIDE  VALVE 


In  fig.  372,  the  valve  is  shown  open  to  exhaust  to  its  full  extent  which 
occurs  during  this  period,  and  at  this  instant  allows  the  steam  in  front 
of  the  fast  advancing  piston  to  escape  from  the  cylinder  with  the  least 
possible  back  pressure. 


Ques.     What  happens  during  pre-release  and  release? 

Ans.  During  pre-release  the  greater  part  of  the  expanded 
steam  is  exhausted,  the  pressure  rapidly  falling  because  of  the 
glow  movement  of  the  piston  at  this  part  of  the  stroke;   during 


COMPRESSION 


Pig.  373. — Position  of  the  valve  at  the  beginning  of  compression.  This  occurs  usually  when 
the  piston  has  travelled  about  three-quarters  of  the  return  stroke,  more  or  less  depending 

■  upon  the  type  of  engine  and  working  conditions.  The  object  of  compression  is  to  introduce 
a  spring  like  back  pressure  to  absorb  or  "cushion"  the  momentum  of  the  reciprocating  parts 
and  bring  them  to  a  state  of  rest  at  the  end  of  the  stroke;  also  to  increase  the  efficiency  by 
saving  some  of  the  exhaust  steam.  Note  that  the  valve  is  in  the  same  position  as  at  pre- 
release (fig.  371)  but  is  moving  in  the  opposite  direction. 


NOTE. — Inside  Lead:  "Experiments  show  that  the  earlier  opening  of  the  exhaust  ports 
is  especially  of  advantage,  and  in  the  best  engines  the  lead  of  the  valve  upon  the  side  of  the  ex- 
haust or  the  inside  lead  is  Vas  to  i/is.  i-  ^-t  the  slide  valve  at  the  lowest  or  highest  portion 
of  the  piston  has  made  an  opening  whose  height  is  V25  to  Vis  of  the  whole  throw  of  the  slide 
valve.  The  outside  lead  of  the  slide  valve  or  the  lead  on  the  steam  side  on  the  other  hand, 
is  much  smaller,  and  is  often  only  1/100  of  the  whole  throw  of  the  valve.  The  outside  lead 
of  the  slide  valve  or  the  lead  on  the  steam  side  on  the  other  hand,  is  much  smaller,  and  is  often 
only  1/100  of  the  whole  throw  of  the  valve — Weishach  (vol.  ii,  p.  296). 

NOTE. — Equalized  Pre-Release  and  Compression.  These  events  occur  at  the  same 
time  when  the  valve  has  no  inside  lap  and  the  correction  of  one  will  likewise  correct  the  other. 
It  is  desired  to  cause  both  these  events  to  occur  earlier  in  the  forward  stroke  and  later  in  the 
return  stroke.  To  accomplish  this,  it  is  necessary  to  give  an  appropriate  positive  inside  lap 
to  the  end  of  the  valve  nearest  the  crank  shaft,  and  an  equal  negative,  inside  lap  to  the  other 
€nd.  The  laps  are  easily  determined  by  means  of  the  Bilgram  diagram.  This  diagram  is 
explained  at  length  in  this  Chapter,  and  should  be  thoroughly  understood  by  those  interested 
in  valve  gears. 


THE  SLIDE  VALVE  ■     201 


release  the  exhaust  pressure  is  always  a  little  higher  than  the 
external  pressure  (that  is,  higher  than  the  pressure  of  the  atmos- 
phere, or  condenser  as  the  case  may  be)  on  account  of  the 
rapidly  advancing  piston  forcing  the  steam  through  the  re- 
stricted passage,  port  and  exhaust  pipe  at  great  velocity.  This 
pressure  is  called  the  back  pressure  of  exhaust^  or  simply  back 
pressure. 

Compression 

Ques.    What  is  compression? 

Ans.  The  closure  of  the  steam  port  to  exhaust  before  the 
piston  has  reached  the  end  of  its  stroke,  thus  shutting  in  a 
portion  of  the  exhaust  steam,  and  by  the  forward  movement  of 
the  piston,   compressing  it  until  pre-admission  begins. 

Ques.     What  is  the  effect  of  compression? 

Ans.  The  rapidly  increasing  back  pressure  due  to  com- 
pression acts  as  a  spring  to  cushion  the  momentum  of  the  moving 
parts,  and  brings  them  to  a  state  of  rest  at  the  end  of  the  stroke.* 

Ques.     On  what  does  compression  depend? 

Ans.  On  the  exhaust  lap  and  angular  advance;  the  greater 
the  lap  or  angular  advance  the  sooner  compression  begins. 

Ques.  Should  compression  begin  at  the  same  point 
in  a  condensing  engine  as  in  a  non-condensing  engine? 

Ans.     No. 

Ques.    Why? 

Ans.  Compression  should  begin  earlier  in  a  condensing  engine 
than  in  a  so  called  high  pressure  or  non-condensing  engine  in 
order  to  get  an  equal  amount  of  cushioning. 


•NOTE. — The  effect  of  compression  is  sometimes  called  cushioning. 


202 


THE  SLIDE  VALVE 


The  compression  curve  of  a  condensing  engine,  because  exhaust  takes 
place  at  a  lower  pressure,  does  not  rise  so  rapidly  as  when  running  non- 
condensing,  hence,  for  equal  cushioning,  compression  must  begin  sooner 
than  in  a  non-condensing  engine. 

Oues.     Does  compression  result  in  a  loss  of  energy? 

Ans.  No,  because  the  power  required  to  compress  the 
confined  steam  is  again  given  out  by  its  expansion  behind  the 
piston  on  the  next  stroke.      In  fact,  there  is  a  "direct  saving, 


LAP- 


-PORT  OPENING 


Fig.  374.— Illustrating  port  opening  and  half  travel  of  the  valve.  The  valve  is  shown  in  dotted 
section  in  its  neutral  position,  and  in  full  section  in  its  extreme  position.  Half  travel  is  equal 
to  the  lap  plus  the  port  opening;  the  latter  being  the  distance  the  steam  edge  of  the  valve 
moves  past  the  steam  edge  of  the  port  during  admission.  This  represents  the  movement 
of  the  valve  on  either  side  of  its  central  or  neutral  position  2ind.=lap-\-port  opening  =A'F 
+  F  A'.    As  drawn,  the  port  opening  is  greater  than  the  port  by  the  amount  G  A'. 

as  the  compressed  steam  is  utilized  to  help  fill  the  clearance 
space  instead  of  filling  it  entirely  with  live  steam. 


Port   Opening 

Oues.    What  is  port  opening? 

Ans.  The  extent  to  which  the  steam  port  is  opened  when 
the  valve  is  at  the  end  of  its  to  and  fro  movement  as  F  A', 
fig.  374. 


THE  SLIDE  VALVE 


203 


Oues.    What  is  the  relation  between  the  port  opening 
and  the  width  of  the  port? 

Ans.     It  may  be  either  greater  or  less  than  the  width  of  the 
port,  as  shown  in  figs.  375  and  376. 

HALF  TRAVEL  (MAXIMUM  ECCENTRICITY) 


PORT  OPENING 

A 


HALF  TRAVEL  (MINIMUM  ECCENTRICITY) 


PORT  OPENING 


Figs.  375  and  376. — Valve. in  extreme  position 
showing:    1,  port  opening  greater  than  the 
^DADT  port,  and  2,  port  opening  less  than  the  port. 

KU  rs  I  With  plain  gear  in  which  the  expansion  is  not 

variable,  the  valve  is  designed  for  a  port  opening  less  than  the  port,  because  for  admission 
less  port  area  is  required  than  for  exhaust,  the  steam  being  admitted  in  good  practice,  at  a 
velocity  of  8,000  ft.  per  minute  and  exhausted  at  6,000  ft.  per  minute.  With  variable 
expansion  gears,  which  vary  the  expansion,  as  later  explained  by  the  method  of  combined 
variable  throw  and  variable  angular  advance,  the'  travel  of  the  valve  is  considerably  reduced 
for  early  cut  off,  hence,  the  port  opening  is  made  more  than  sufficient  at  late  cut  off  as  in 
fig.  375,  in  order  that  the  reduced  opening  for  early  cut  off  as  in  fig.  376  will  not  be  too  small. 


204 


THE  SLIDE  VALVE 


In  the  case  of  a 
throttling  engine 
where  the  travel  of 
the  valve  does  not 
change,  the  port 
opening  may  be  less 
than  the  width  of 
the  port,  as  in  fig. 
376,  because  ad- 
mission does  not  re- 
quire as  much  port 
opening  as  exhaust. 
"W  ith  automatic  cut 
off  engines,  when 
the  cut  off  is  short- 
ened by  the  method 
of  combined  variable 
angular  advance  and 
variable  throw,  evi- 
dently there  must 
be  an  excess  of  port 
opening  (as  in  fig. 
375)  for  a  late  cut 
off,  otherwise  at 
early  cut  off  it 
would  be  insuffi- 
cient for  admission, 
on  account  of  the 
considerable  de- 
crease in  valve 
travel. 

Oues.  What 
is  the  com- 
parison be- 
tween large 
and  small  port 
opening? 

Ans.  A  large 
port  opening 
permits  very 
early  cut  off 
without  choking 
the     admission. 


THE  SLIDE  VALVE  205 


On  account  of  the  greater  velocity  of  the  valve,  the  events  of  the 
•  stroke  such  as  cut  off  release,  etc.,  are  more  sharply  defined;  in 
other  words,  there  is  less  wire  drawing.  These  features  are 
offset  somewhat  by  the  increased  wear  of  the  valve  and  larger 
valve  gear  necessary  to  secure  the  increased  valve  travel. 


Travel 

Oues.    What  is  the  travel*  of  a  valve? 

Ans.     The  extent  of  its  to  and  fro  movement  as  shown  in 
fig.  377. 

Here  the  valve  is  shown  in  full  lines  at  one  end  of  its  travel,  and  in  dotted 
lines  at  the  other  end,  the  travel  being  the  distance  M"  M'. 

Oues.     How  is  the  travel  obtained? 

Ans.     From  the  lap  and  the  port  opening. 

Travel  of  valve  =  twice  the  lap -{-twice  the  port  opening. 

In  fig.  374,  the  valve  is  shown  in  dotted  lines  in  its  neutral  position  M 
and  in  full  lines  at  one  end  of  its  travel  M'. 

It  is  evident  from  the  figure  that  the  valve  has  moved  a  distance  to  the 
right  equal  to  the  lap  A  F,  plus  the  port  opening  F  A'. 

Now  to  admit  steam  to  the  other  end  of  the  cylinder  through  the  port 
F' G',  the  valve  must  move  an  equal  distance  to  the  left  of  its  neutral 
position  M,  that  is  a  distance  equal  to  M  M"  in  fig.  377.  Hence,  the  travel 
equals  twice  the  lap  plus  twice  the  port  opening.  The  full  travel  M"  M'  is 
shown  in  fig.  377. 

Oues.    What  is  over  travelf? 


*NOTE. — In  the  year  1836,  the  word  travel  was  used  in  a  different  sense  from  the  present 
meaning.  According  to  Wansbrough,  in  order  to  keep  the  steam  on  the  piston  as  long  as 
possible,  the  valve  moved  nearly  one-half  inch  beyond  the  port  at  each  end  or  "over  opened" — 
this  distance  or  movement  beyond  the  port  was  called  the  travel. 

tNOTE. — The  term  over  travel  is  used  by  some  writers  to  denote  the  distance  the  steam 
edge  of  the  valve  moves  beyond  the  exhaust  edge  of  the  steam  port  in  opening  it.  The  author 
prefers  to  define  it  with  respect  to  the  seat  limit. 


206 


THE  SLIDE  VALVE 


Ans.     The  extent  to  which  the  steam  edge  of  the  valve  moves 
beyond  the  seat  Hmit,  as  A  E  or  E'  D,  fig.  377. 

Oues.     What  is  the  object  of  over  travel? 

Ans.     To   preserve   uniform   wear   of   the   seat,    and   reduce 
the  unbalanced  load  on  the  valve. 


UNEAR   ADVANCE 


LAP 


-LEAD 


Fig.  378. — Showing  valve  in  its  position  of  linear  advance.  When  the  piston  is  at  the 
beginning  of  the  stroke,  the  yalve  must  be  at  a  distance  from  its  neutral  position  equal 
to  the  lap  plus  the  lead.  The  valve  is  shown  in  solid  black  in  its  linear  advance  position,  and 
in  dotted  section  in  its  neutral  position. 


Linear  Advance 

Oues.    What  is  the  linear  advance  of  a  valve? 

Ans.     It  is  the  distance  the  valve  has  moved  from  its  neutral 
position,  when  the  piston  is  at  the  beginning  of  the  stroke. 

Owes.     Upon  what  does  linear  advance  depend  ?  * 


*NOTE. — It  should  be  remembered  that  the  word  lap  unqualified  always  means  outside  or 
steam  lap.    The  same  is  true  of  lead. 


THE  SLIDE  VALVE 


207 


O  o 


o.  a 


si 


93   S  B 


■11* 


aj  o  a>  ^  ^  S.2i_§ 
J2J£^  cj  oj  c  ss  9 


1^  t- 

II 

tu  e3 


o  OT3  ij'a  o  I 


1§ 


I   §-0   J-TJ  W   "3   2 

I  5  «  *  «  c  «3  5 

)  3   t^   a?  t<.3   <u  3 


-^•3    "2    "i 


-a-o 


3:= 


o    3    3    «    2 
U    3    3    «    3 


-o -a -a -0-3 

O)    OJ    «  O    0--3 

t«  tiC  bc  bc  tc  5  ,— 

c  a  3  c  c  05  ^ 

eS  cU   33  oj  ea  g!  5 

o  ol3  «  o  J5  «^ 

3  3  3  3  3.SJ2  Z 


^ 

2 

-0-0 

T3-0 

fe 

1 

reduced 
reduced 
reduced 

1 

1 

-a 

^1 

3  03 
3   3 

II 

a  a 
3  3 

.2  § 

-a  X 

03  m 


1-2 
II 


Ans.     On  the  amount  of  lap 
and  lead. 

Thus  in  fig.  378,  the  valve  has 
moved  from  its  neutral  position  a 
distance  MM',  equal  to  its  linear 
advance.  The  valve  in  its  neutral 
position  is  shown  in  dotted  lines 
and  in  its  linear  advance  position 
in  full  section. 

From  the  figure  it  is  clear  that: 
linear  advance  =  lap* -\-lead. 


Early  Cutoff 

Oues.  How  may  the  cut 
off  be  varied? 

Ans.  By  changing  both  the 
angular  advance  and  throw  of  the 
eccentric;  the  greater  the  angular 
advance  and  shorter  the  throw^ 
the  earlier  the  cut  off. 

In  order  not  to  unduly  affect  the 
other  events  of  the  stroke,  the  valve 
gear,  as  will  be  later  explained,  is 
arranged  to  increase  the  angular  ad- 
vance simultaneously  as  the  throw  is 
reduced,  this  being  called  the  method 
of  combined  variable  angular  advance 
and  variable  throw. 

Oues.  What  objection  is 
there  to  shortening  the  cut 
off  by  the  above  method? 


•NOTE.— See  note  on  page  206. 


208 


THE  SLIDE  VALVE 


Ans.  The  shorter  the  travel,  the  less  the  port  opening,  hence 
for  very  early  cut  off  there  is  insufficient  port  opening  for 
admission,  moreover,  pre-release  begins  earlier  and  compression 
later. 

Oues.    How  may  the  first  objection  be  overcome? 


Fig.  379. — The  Allen  valve.  The  supplementary  passage  is  for  double  admission  which  is 
desirable  on  locomotives  fitted  with  link  motion  as  they  are  usually  run  with  short  cut  ofis, 
-.jid  the  action  of  the  link  under  these  conditions  gives  very  little  port  opening. 


Fig.  380. — The  Allen  valve  in  lead  position  showing  double  admission.  It  should  be  noted 
that  the  second  admission  through  the  supplementary  port,  depends  on  the  length  of  the 
seat  which  forms  the  lap. 


THE  SLIDE  VALVL 


209 


Ans.  By  providing 
a  supplementary  pas- 
sage in  the  valve  for 
the  admission  of  steam, 
as  shown  in  fig.  379, 
which  represents  the 
Allen  valve,  used 
principally  on  loco- 
motives. This  passage 
terminates  in  the  lap 
at  B  F  and  B'  F'. 
The  seat  limit  is  such 
that  A  F,  the  lap  of 
the  valve  equals  B'  E', 
which  acts  as  lap  for 
the  supplementary 
passage.  As  the  valve  • 
moves,  for  instance,  to 
the  right,  A,  passes  F, 
at  the  same,  time  that 
B',  passes  E',  hence, 
steam  is  admitted 
simultaneously  by  both 
ends  of  the  valve  as 
shown  in  fig.  380.  The 
effect  is  the  same  as  an 
ordinary  valve  moving 
at  double  speed. 
Following  the  further 
movement  of  the  valve, 
it  will  be  seen  that 
the  valve  continues  to 
open  the  port  FG   at. 


210 


THE  SLIDE  VALVE 


double  speed  until  it  has  reached  the  position  shown  in  fig.  381. 
Here  the  total  port  opening  is  F  A+B  C.  This  opening  will 
not  be  increased  by  any  further  movement  of  the  valve  in 
traveling  to  its  extreme  position  as  shown  in  fig.  382,  on  account 
of  the  closing  of  the  supplementary  port.  In  this  position  the 
opening  F  A  (fig.  382)  =F.A  (fig.  381)+  B  G. 


Figs,  384  to  386. — Allen  valve  with  negative  lap.  When  the  valve  has  a  large  steam  lap,  it 
is  not  difficult  to  keep  the  opening  of  supplementary  port  within  this  lap,  and  even  to  leave 
a  small  positive  inside  lap  I,  fig.  385.  but  when  the  main  lap  s  is  smaller,  or  the  width  h  is 
increased,  there  will  be  a  negative  lap  to  the  supplementary  port  as  at  /,  fig.  386.  The 
result  is,  that  during  a  brief  time  a  passage  is  opened  from  one  end  of  the  cylinder  to  the 
other,  with  some  tendency  to  modify  the  exhaust  operation.  Thus  in  fig.  386  the  valve 
is  at  the  distance  /'  and  moving  toward  the  right.  Compression  has  begun  in  the  left  end 
of  the  cylinder,  and  now  steam  which  has  not  yet  been  released  in  the  right  end  is  about 
to  flow  over  and  increase  the  pressure  and  the  amount  of  the  clearance  steam  in  the  other 
end.  This  action  will  occur  while  the  valve  travels  through  the  distance  21,  but  since  it 
moves  rapidly  near  neutral  position  and  the  openings  involved  are  small,  the  effect  upon 
the  steam  distribution  will  be  small. 

If  the  steam  ports  be  enlarged  as  shown  in  fig.  383  they  would  be  com- 
pletely opened  when  the  valve  reaches  the  extreme  position.  This  would, 
however,  necessitate  a  somewhat  longer  valve. 

How  to  Design  a  Slide  Valve. — The  method  of  designing  a 
valve  as  here  given  is  so  simple  that  it  should  present  no  difficulty, 
and  the  engineer  who  learns  and  understands  the  method  will 
have  no  trouble  in  designing  and  setting  a  valve. 


THE  SLIDE  VALVE  211 

r  Although  the  dimensions  of  a  valve  may  be  worked  out  by 
^mathematics,  it  is  essentially  a  drawing  board  problem,  and  is 
better  solved  in  that  way.  In  solving  the  problem  graphically, 
use  is  made  of  a  valve  diagram  for  obtaining  the  lap,  angular 
advance,  etc.  There  are  a  number  of  these  diagrams  of  which 
Bome  writers  employ  the  one  devised  by  Zeuner.  The  author 
considers  the  Bilgram  by  far  the  best  and  simplest  and  it  is  the 
one  here  used.  The  Zeuner  diagram  is  objectionable  in  that 
it  is  a  **cut  and  try"  method.* 

The  following  example  will  serva  to  illustrate  the  application 
of  the  Bilgram  diagram. 

Example, — A  7X7  engine  is  to  be  run  at  450  revolutions  per  minute. 
What  are  the  principal  dimensions  of  the  slide  valve  and  ports  for  a  steam 
velocity  of  8,000  feet  per  minute  through  the  port  opening  and  6,000  feet 
through  the  ports?  Lead  He  inch,  cut  off  %,  release  .9  stroke,  length 
of  ports  .8  the  diameter  of  the  cylinder,  and  length  of  connecting  rod  2}/^ 
times  the  stroke. 

1,     Find  area  and  dimensions  of  port  opening  and  port. 

area  piston  m  sq.  ins.  y^piston  speed  in  feet 
area  port  opening  in  sq.  ins.  = 


8,000 
(72 X. 7854)  X  (450XVi2X2) 


=  2.53  sq.  in. 


8,000 

Since  the  velocity  of  the  steam  through  the  port  is  reduced  to  6,000  feet 
per  minute,  it  is  made  larger  than  the  port  opening  in  the  proportion  of 
8,000-7-6,000,  or 

8 
area   of  port=  2,5SX —  =  3. 37  sq.m. 
6 


*NOTE. — Mr.  Halsey  in  his  admirable  book  on  Slide  Valve  Gears,  says,  in  criticising  the 
Zeuner  diagram:  "The  leading  data  that  are  given  in  designing  a  valve  motion  are  the  point 
of  cut  off,  the  port  opening,  and  the  lead  of  the  valve  (not  the  lead  angle  of  the  crank,  as  is 
often  conveniently  assumed).  It  is  the  radical  defect  of  the  Zeuner  diagram  that  none  of  these 
dimensions  cfen  be  laid  off  from  known  points.  The  lead  must  be  laid  off  from  an  unknown 
point  of  the  center  line,  and  the  port  opening  from  an  unknown  point  on  an  unknown  line. 
Finally,  through  these  unknown  points  and  the  center  of  the  shaft  the  valve  circle  is  to  be 
drawn  from  an  unknown  center  and  with  an  unknown  radius.  Under  these  circumstances 
the  result  sought  is  found  only  through  blind  trial."  Continuing  he  says:  "With  Mr.  Bil- 
gram's  method  all  this  is  changed.  The  lead  is  laid  off  from  a  fixed  Une.  the  port  opening  from 
a  fixed  point,  and  the  cut  off  position  of  the  crank  is  located.  The  lap  circle  is  then  drawn 
tangent  to  these  lines,  and  the  problem  is  solved.  Moreover,  the  awkward  conception  of  the 
backward  rotation  of  the  crank  is  obviated.  Finally,  these  marked  advantages  are  not  ac- 
companied by  any  compensating  disadvantages  whatever."  The  author  is  in  accord  with  the 
above  views. 


212 


THE  SLIDE  VALVE 


The  length  of  the  ports  is  made 
.  8  the  cyHnder  diameter,  or 

Length  of  ports  =  7  X  .  8  = 
5.6,  say  53^  ins. 

Width  of  steam  ports 

=  area -i- length 
or 

3.37-^53ij=  .612,  say  5^  in. 
Width  of  port  opening  = 


^X 


6,000 
8,000 


=  15^ 


!,  say  yi  m. 


2.  Find  the  position  of  the 
crank  for  3/^  cut  off. 

In  fig.  387  draw  a  horizontal 
line,  and  near  one  end  describe  a 
circle  with  any  radius  as  O  E. 
Measure  off  the  length  of  the 
connecting  rod  A  E  =  5X0  E, 
and  A  B  =2X0  E.  A  B,  then  is 
the  length  of  the  stroke. 

Find  the  position  of  the  cross 
head  F,  when  the  piston  is  at  % 
stroke  by  taking  A  F  =  3^  A  B. 
With  F,  as  center  and  radius 
F  D  =  A  E,  describe  an  arc 
cutting  the  circle  in  C.  This  is 
the  position  of  the  crank  pin 
when  the  piston  is  at  %  stroke. 

3.  Find  the  lap,  linear  ad^ 
vance  and  travel  of  the  valve* 

Use  is  here  made  of  the  Bil- 
gram  diagram,  and  the  succes- 
sive steps  in  its  application  are 
as  follows : 

a.  A  horizontal  line  K  N,  is 
drawn,  and  the  crank  position 
for  %  cut  off  transferred  from 
fig.  387  to  fig.  388. 

b.  Draw  a  line  M  S  parallel  to 
K  N  at  a  distance  above  {1{q  in.) 
equal  to  the  lead;  M  S,  then  is 
the  lead  line. 


I 


THE  SLIDE  VALVE 


213 


c.  With  a  radius  O  A,  equal  to  the  port  opening  (3/2. in.),  describe  the 
port  opening  circle. 

d.  Now,  find  by  trial  the  radius  E  F,  and  center  E,  of  a  circle  that  shaU 
be  tangent  to  the  lead  line  M  S,  the  port  opening  circle,  and  the  cut  off 
line  O  C.    The  radius  BF,  of  this  circle  is  the  outside  lap. 

e.  Draw  E  H  perpendicular  to  K  N,  then  the  distance  E  H  is  the  linear 
advance. 

J.  Now  by  the  method  of  fig.  387,  find  the  crank  position  for  release  at 
.9  stroke.  In  fig.  388,  draw  this  crank  position  O  C,  and  a  circle  tangent 
to  it  with  center  E  G     The  radius  E  G,  of  this  circle  is  the  inside  lap. 


COMPRESSION 


EF=  OUTSIDE   LAP 
EG=^  INSIDE    LAP 
LINEAR    ADVANCE 
yie    LEAD 

ANGULAR    ADVANCE 


Fig.  388. — The  Bilgram  diagram  for  finding  the  lap,  angular  advance  travel,  etc.,  of  the  slide 
valve.     With  this  diagram,  any  valve  problem  may  be  easily  and  quickly  solved. 

g.  A  second  tangent  O  C,  to  this  circle  gives  the  crank  position  for 
compression. 

Measuring  the  diagram,  the  dimensions  for  the  valve  are 
Outside  lap  =  }/2  in.  Linear  advance  =  ^e  ^^• 

Inside  lap  =^2^^-  TrcCvel    of    valve  =  2  ins. 


With  the  dimensions  just  obtained  and  the  given  data,  the 
valve  and  ports  may  be  laid  down  in  the  following  manner: 


214 


THE  SLIDE  VALVE 


1,  Find  length  of  valve  face. 

Length  of  valve  face  =  outside  lap-\-width  of  steam  port-\- 
insidelap  =  }4-i-^+^2  =  '^'H2 

In  fig.  389  the  steam  port  and  one  end  of  the  valve  is  drawn  in  neutral 
position  giving  length  of  valve  face. 

2.  Find  width  of  exhaust  port. 

This  is  done  as  shown  in  fig.  390.     Draw  a  horizontal  line  representing 

NEUTRAL  POSITION 


Fig.  389. — How  to  lay  out  the  slide  valve.  I.  With  the  dimensions  obtained  by  the 
Bilgram  diagram  the  length  of  the  face  is  determined  by  sketching  one  end  of  the  valve 
in  its  central  or  neutral  position  as  here  shown. 


the  valve  seat  and  lay  off  the  steam  port  FG.  =  ^  in.     Next  lay  off  the 
bridge  G  H  *  making  it  }^  inch  wide. 

Draw  one  end  of  the  valve  in  its  extreme  position  for  admission, 
this  position,  the  distance  FA,  is  equal  to  the  port  opening. 


For 


*NOTE. — The  width  of  the  bridge  depends  on  the  size  and  thickness  of  the  cylinder 
casting:  it  should,  of  course,  be  amply  wide  to  give  a  steam  tight  joint  when  covered  by  the 
valve  face. 


THE  SLIDE  VALVE 


215 


As  steam  is  being  exhausted  from  the  other  end  of  the  cylinder  when 
the  valve  is  in  this  position,  it  is  evident  that  the  exhaust  opening  B  H', 
must  equal  the  width  of  the  steam  port  so  as  not  to  choke  the  exhaust. 
Hence,  lay  off  B  H'  =  F  G,  and  draw  the  bridge  H'  G'  =  G  H.  H  H'  then 
is  the  required  width  for  the  exhaust  port. 

2.  Locate  the  seat  limit. 

Draw  one  end  of  the  valve  in  its  extreme  position  for  exhaust  as  shown 

EXTREME  POSITION 


PORT  OPENING 


Fig.  390. — How  to  lay  out  the  slide  valve.  II.  The  width  of  the  exhaust  port  is  obtained  by 
sketching  one  end  of  the  valve  in  extreme  position  for  admission.  Evidently  H',  must  be 
so  located  that  B  H'  =F  G,  in  order  not  to  choke  the  exhaust. 


in  fig.  391.  To  do  this,  lay  off  G  B',  equal  to  the  exhaust  lap  and  draw  the 
dotted  line  which  is  the  neutral  position  of  the  exhaust  edge  of  the  valve. 
For  the  extreme  position  this  edge  moves  to  the  left  a  distance  B'  B,  equal 
to  one-half  the  travel  of  the  valve  (  =  1  in.,  see  page  213). 

Valve  end  is  now  drawn  in  its  extreme  position  thus  found,  and  the  seat 
limit  E,  (fig.  391)  may  be  located  at  any  point  between  A  and  B,  which  gives 
sufficient  seal  E  B.  to  prevent  leakage  of  the  steam  and  a  clearance  A  E, 


216 


THE  SLIDE  VALVE 


for  over  travel.  In  this  case  the  over  travel  is  taken  at  one-half  inch.  It 
is  recommended  for  unbalanced  valves  that  the  seal  E  B,  be  made  no  more 
than  is  necessary  for  a  steam  tight  joint  to  reduce  the  unbalancing. 

4,  Draw  valve  seat  and  valve  in  neutral  position. 

From  the  dimensions  already  obtained  the  valve  seat  is  laid  down  as 
shown  in  fig.  392.  The  two  faces  of  the  valve  A  B  and  C  D,  are  located 
in  neutral  position  and  the  remainder  of  the  valve  drawn. 

EXTREME  POSITION 


•5EAT  LIMIT 


Pig.  391. — How  to  lay  out  the  slide  valve.  III.  The  seat  limit  is  obtained  by  sketching  one 
end  of  the  valve  in  extreme  position  for  exhaust  as  shown  and  locating  the  seat  limit  E 
between  A  B,  at  some  point  which  will  give  sufficient  contact  E  B,  for  a  tight  joint,  this 
distance  being  called  the  seal. 


The  dimension  now  needed  is .  the  distance  B  C,  between  the  exhaust 
edges.    After  measuring  this  distance  it  should  be  checked  as  follows: 

Distance   between   exhaust    edges  =  width    of    exhaust    port +2  X  width 
of  bridge  —  2  X  exhaust  lap.     That  is 

BC  =  HH'+2GH  — 2  GB 
=  1%  +2X3^  — 2%  =  2i^2. 


THE  SLIDE  VALVE 


217 


S^ 


05.y 


± -OS  a 

I  si 

OT   O    W 

ill 

03.S  a> 
CQt3  o, 


ii 


"So 


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c  s 

«f, 

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0)  -M 

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e: 

^^ 

E:5 
o 

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11 

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w      2       (U 

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.-«>  to  to  3.*^ 
,  rt       o  c  *-<  "^-i  "t:^  O 


rt  o       ftrt  i 


bod      5  I-.  "^ 


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«  o  I 


DOT      «        O   to 


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s«g5 


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!*  a;  c  >  c* 
7coS7^^^-^-2 


b  gj^b-is  g.Sb  o 


218 


THE  SLIDE  VALVE 


Defects  of  the  Slide  Valve 

1.  A  small  increase  in  the  port  opening  requires  a  great  increase 
in  lap  and  travel. 

A  valve  hciving  the  proportions  of  the  one  in  the  foregoing  example, 
would  be  suitable  for  an  engine  with  a  fixed  cut  off.  If  it  were  designed 
for  a  variable  cut  off  engine,  the  port  opening  should  at  least  be  equal  to 
the  width  of  the  port,  or  somewhat  greater  to  provide  for  sufficient  opening 


^/4  CUT  OFF 


I  J    TRAVEL  FOR  ^2  IN.    \^ 
i     I      PORT  OPENING  )\ 


-  TRAVEL  FOR  V^  IN,  PORT  OPENING   — 

Fig.  393. — Defects  of  the  slide  valve:  A  small  increase  in  the  port  opening  requires  a  large 
increase  in  the  travel,  and  additional  lap.  In  the  diagram  increasing  the  port  opening  O  A, 
to  O  A',  ^  inch,  increases  the  travel  K  N,  to  K'  N',  or  l^^inches. 

at  early  cut  off.  The  effect  of  this  is  seen  by  drawing  another  diagram 
as  in  fig.  393,  increasing  the  port  opening  from  one-half  to,  say,  three-fourths 
inch. 

In  the  diagram,  the  original  proportions  are  shown  in  dotted  lines  from 
which  it  is  seen  that  for  an  increase  A  A',  of  one-fourth  inch  of  port  opening 
the  travel  K  N,  is  increased  to  K'  N',  or  lYs  inches. 


THE  SLIDE  VALVE 


219 


In  fig.  394  the 
original  valve  is 
shown  in  cross  sec- 
tion and  one  having 
the  new  proportions 
in  dotted  lines. 
Comparing  the  two, 
it  is  seen  that  the 
exhaust  cavity  is 
larger.  This  to- 
gether with  the 
additional  lap,  con- 
siderably increases 
the  length  of  the 
valve,  thus  exposing 
a  larger  unbalanced 
area  to  the  action 
of  tne  steam. 

Quite  as  objec- 
tionable is  the  in- 
crease in  the  travel, 
requiring  as  it  does, 
larger  ports  for 
moving  the  valve. 


2.  The  travel 
is  excessive  when 
the  valve  is  de- 
signed for  an 
early  cut  of;  con- 
siderable lap  is 
required. 

The  effect  of 
shortening  the  cut 
off  from  three- 
fourths  to,  say,  one- 
half  stroke  is  shown 
in  fig.  395.  The 
full  lines  show  the 
proportions  for 
three-fourths  cut 
off,  and  the  dptted 
lines    for    one-half 


220 


THE  SLIDE  VALVE 


cut  off.     By  measuring  the  diagram  it  is  found  that  the  travel  has  increased 
from  2  ins.  to  3iJ^2  i^s.,  also  the  lap  has  increased  from  3^  to  IJ^. 

The  size  of  the  valve  is  greatly  increased  as  shown  in  fig.  177.  The  three- 
fourths  cut  off  valve  is  shown  in  cross  section  and  the  one-half  cut  off  valve 
in  dotted  lines.  The  valve  seat  for  the  latter  being  shown  in  dotted  cross 
section. 

3.  On    account   of  the    large   proportions   and   excessive   travel 
necessary,  the  slide  valve     ^\^^    CUT    OFF  A  ^  CUT  OFF 

is  considered  undesir- 
able for  cut  offs  shorter 
than  one-half  stroke.'^ 


K- 


TRAVEL  FOR  ^/4  CUT  OFF 


TR/^V&LFOR  Va  CUT  OFF 


Fig.  395. — Defects  of  slide  valve:  The  traveCis  excessive  when  the  valve  is  designed  for  an  early 
cut  off;  considerable  lap  is  required.  The  diagram  shows  the  large  increase  in  travel  necessary 
in  shortening  the  cut  off  from  %to  Y^  stroke,  and  also  why  the  slide  valve  is  not  suitable  for 
cut  offs  shorter  than  H  stroke. 

In  general,  to  keep  the  proportions  of  a  valve  within  limits,  for  a  short 
cut  off,  the  ports  must  be  made  as  long  as  possible  sc  as  to  reduce  the 


*NOTE. — It  should  be  understood  that  this  means  the  cut  off  with  full  travel.  Any 
valv^  may  be  made  to  cut  off  shorter  by  reducing  the  travel  as  before  explained  but  this  is  at 
the  expense  of  reducing  the  port  opening. 


THE  SLIDE  VALVE 


221 


width  and  thus  secure  the  proper  admission  with  a  minimum  of  valve 
movement. 

The  Allen  valve  requires  only  one-half  the  lap  and  travel  of  the  9rdinary' 
valve  as  shown  in  the  diagram  fig.  396*,  the  diagram  for  the  Allen  valve 
being  shown  in  full  lines,  the  other  dotted.  In  figs.  397  and  398  are  shown 
the  proportions  required  for  the  ordinary  valve  cutting  off  at  three-fourths 
and  one-half,  and  the  Allen  valve  with  one-half  cut  off.     M,  is  the  half 


»/^CUT  OFF 


TRAVEL  ORDINARY  VALVE 


Fig.  396. — Comparative  diagrams  showing  travel  of  AUeii  and  plain  slide  valve.    The  Allen 
valve  requires  only  half  the  travel  and  half  the  lead  of  the  plain  slide  valve. 


travel  required  for  three-fourths  cut  off,  M',  for  one-half  cutoff,  and M", 
for  one-half  cut  off  with  the  Allen  valve.  The  figures  are  intended  to  show 
by  comparison  the  undesirable  features  of  the  ordinary  valve  at  early  cut  off. 


*NOTE. — In  the  diagram  the  port  opening  arc  A  B,  is  taken  with  radius  one-half  smaller 
than  A'  B',  the  port  opening  arc  of  the  ordinary  valve  because  double  admission  is  secured  with 
the  Allen  valve. 


222 


THE  SLIDE  VALVE 


The  full  benefit  to  be  derived  from  the  Allen  valve  may  be  obtained  by 
so  modifying  the  steam  ports,  as  shown  in  figs.  383  and  398,  that  the 
supplementary  ports  are  not  closed  when  the  valve  is  in  the  extreme 
positions. 


SIZE  FOR 
5^  CUT  OFF 


1 5\ZL  FOR 

'        '/4  CUT  OFF 


//////////■ 


Figs.  397  and  398. — Showing  sizes  of  valve  for  K  and  M  cut  off  corresponding  to  the  diagram 
fig.  396.  The  considerable  increase  in  the  length  of  valve  and  seat  necessary  for  the  shorter 
•cut  off  as  indicated  by  the  dotted  lines  should  be  noted.  Fig.  398  shows  the  Allen  valve  with 
modified  steam  ports  for  y^  cut  off  as  compared  with  the  plain  slide  valve  for  >^  and  %  cut  off. 

4.  For  a  short  cut  off,  release  and  compression  occur  too  early. 
This  is  illustrated  in  the  diagram  fig.  399.    A,  A',  and  B,  B',  are  the  cranir 


THE  SLIDE  VALVE 


223 


positions  of  release  and  compression  for  three-fourths  and  one-half  cut  off 
respectively.  Either  may  be  corrected  by  the  addition  of  positive  or  nega- 
tive inside  lap,  but  it  must  be  evident  that  to  correct  one,  will  cause  the 
other  to  occur  still  more  prematurely. 


5.  For  variable  expansion,  the  port  opening  is  inadequate,  and 
release  and  compression  occur  too  early  at  short  cut  off. 


COMPRESSION  \ 
(•/2CUT  OFF)   (  BOTH 
/    Too 
^,       RELEASE      (  50DN 

^    r  (5i  CUT  off); 

"^B^  COMPRESSION 
i^A  CUT  OFF) 

RELEASE 

C ^4  CUT  off; 


Fig.  399. — Defects  of  the  slide  valve:  For  a  short  cut  off  release  and  compression  occur 
too  early.  The  diagram  shows  the  effect  on  release  and  compression,  of  changing  the  cut  off 
from^^to^.  Either  may  be  corrected  with  positive  or  negative  inside  lap  but  the  error 
of  the  other  will  be  correspondingly  magiiified. 


As  will  be  explained  in  detail  in  a  later  chapter,  the  cut  off  may  be  varied 
by  the  method  of  combined  variable  angular  advance  and  variable  throw , 
as  is  done  mainly  on  engines  having  shifting  or  swinging  eccentrics 
known  popularly  as  "automatic  cut  off  engines." 


224 


THE  SLIDE  VALVE 


Assume  latest  cut  off  at  J^  stroke  and  that  TT,  is  greatest  travel  mechani- 
cally feasible.  Draw  O  C  =  %  cut  off  and  describe  travel  circle  with  radius 
O  T,  and  on  this  circle  draw  lap  circle  tangent  to  O  C,  and  lead  line.  The 
corresponding  port  opening  A'  B',  as  seen,  is  considerably  in  excess  of  the 
required  or  normal  opening  A  B. 

Now  since  the  travel  is  reduced  as  the  cut  off  is  shortened  a  series  of  lap 
circles  R,  R',  R",  will  appear  in  the  diagram  on  a  Hne  M  S,  drawn  parallel  to 

fCUT  OFF  FOR  NORMAL 
l      PORT  OPENING 


CUTOFF 


J4  CUT  OFF. 


MAXIMUM 
TRAVEL 


MINIMUM 
TRAVEL 


A' 
A 
A" 


b'^ 


.^-^djEXCESS  PORT  OPtiNING 
P  lAT  LATE  CUT  OFF 

^NORMAL  PORT  OPENING 


^/INADEaUATE    PORT  OPENING 
VAT  EARLY  GUT  OFF 


Fig.  400. — Defects  of  the  slide  valve  5. — For  variable  expansion  the  port  opening  is  in- 
adequate, and  release  and  compression  occur  too  early  at  short  cut  off.  The  diagram  shows 
the  effects  of  changing  the  cut  off  from  M  to  >^  by  the  method  of  combined  variable  angular 
advance  and  variable  travel.  Evidently,  when  variable  expansion  is  thus  obtained,  the  travel 
of  the  valve  should  be  as  great  as  possible  in  "full  gear,"  because  of  the  decreasing  port 
opening  with  shortening  of  the  cut  off.  From  the  diagram,  it  is  also  clear  that  the  shorter 
the  full  gear  cut  off,  the  larger  the  port  opening  at  earliest  cut  off. 

the  lead  line   (assuming  constant  lead).    Thus  lap  circle  R',  for  normal 
port  opening,  gives  a  cut  off  O  C\  near  one  half  stroke. 

Ordinarily  the  most  economical  cut  off  is  at  }4  stroke  (non-condensing),  the  lap  circle  R", 
in  the  diagram  giving  this  cut  off.  The  port  opening  as  seen  for  }4  cut  off  is  reduced  to  A" 
B",  being  about  one  half  less  than  the  required  amount  A  B. 

Accordingly  the  operation  of  automatic  cut  off  engines  at  early  cut  off  is  characterized 
by  a  sloping  admission  line  on  the  indicator  card  the  pressure  drop  reducing  the  efficiency. 
Moreover  release  and  compression  occur  as  the  cut  off  is  shortened,  being  entirely  too  early 
at  }4  cut  off.  In  the  diagram  these  events  are  represented  by  the  crank  position  O  R,  O  R' 
and  O  R",  corresponding  to  cut  offs  O  C,  O  C,  and  O  C*  respectively. 


THE  VALVE  GEAR  225 


CHAPTER    5 
THE  VALVE   GEAR 


Oues..    What  is  the  valve  gear? 

Ans.  The  mechanism,  or  combination  of  parts  by  which  a 
reciprocating,  or  to  and  fro  motion  is  imparted  to  the  valve  from 
the  rotary  motion  of  the  shaft.  The  simplest  form  of  valve 
gear  consists  of: 

1.  Yoke; 

2.  Stem; 

3.  Guide; 

4.  Eccentric  rod ; 

5.  Eccentric  strap; 

6.  Eccentric.      -.^^^..^'/-^^Ir.-^ 

These  parts  are  shown  assembled  in  fig.  401. 

The  Valve  Yoke. — The  valve  is  held  in  position  by  a  yoke 
which  consists  of  a  rectangular  band  (fig.  402)  which  surrounds 
the  upper  part  of  the  valve.  The  latter  is  indicated  by  dotted 
lines  illustrating  the  position  of  the  valve  with  respect  to  the 
yoke. 

The  fit  between  the  yoke  and  valve  is  such  that  the  latter  is  free  to  move 
up  or  down  and  thus  adjust  itself  to  the  seat.  At  A,  is  a  slight  enlargement 
to  receive  the  valve  stem. 

In  some  cases  the  yoke  is  omitted  and  the  stem  attached  direct 
to  the  valve  as  shown  in  fig.  403. 


226 


THE  VALVE  GEAR 


The  valve  is  retained  in  place  by 
the  nuts  A  and  B,  by  which  the  length 
of  the  stem  is  adjusted  in  setting  the 
valve.  In  fig.  402,  the  adjustment  of 
the  stem  is  at  A. 


The  Valve  Stem.— This  is 
usually  made  of  steel  and  serves 
to  transmit  the  motion  of  the 
eccentric  rod  to  the  valve.  Fig. 
402  shows  the  type  stem  used 
with  a  yoke,  and  fig.  403  the 
form  used  without  yoke.  From 
figs.  404  to  406  it  is  seen  that  a 
valve  stem  consists  essentially  of : 

1.'  A  threaded  section  A  form- 
ing a  connection  for  yoke  or 
valve,  and  providing  for  adjusting 
the  length  of  the  stem  in  setting 
the  valve; 

2.  A  cylindrical  section  B, 
which  passes  out  of  the  steam 
chest  through  the    stuffing    box; 

3.  An  enlarged  section  C  to 
secure  sufficient  bearing  area  for 
the  guide; 

4.  A  pin  connection  D  for  the 
eccentric  rod. 


NOTE. — The  valve  stem  is  designed  to  move 
the  valve  under  the  most  unfavorable  conditions. 
A  short  rule  is:    diam.  stem  =1/3  diam.  cylinder 
diam.    piston    rod.        Seaton's    formula. 

"^  ~  -^1 ,  where  p  =  boiler  pressure;  L  and  B. 


■f 


length  and  breadth  of   (slide)  valve;  F  =  10,000, 
for  long  iron  stem  =  12,000  for  long  steel  stem. 


THE  VALVE  GEAR 


227 


^oy<<z 


Fig.  402. — The  valve  yoke,  or  rectangular  frame  which  embraces  the  box  shaped  section 
of  the  valve,  and  to  which  the  valve  stem  is  attached.  The  valve  is  shown  in  dotted  lines  to 
indicate  the  position  of  the  yoke. 


5TEM 


Fig.  403. — Method  of  connecting  the  valve  stem  to  the  valve  without  a  yoke.  The  stem 
passes  through  a  circular  section  cast  in  the  valve,  being  adjustable  by  means  of  the  nuts 
A,  B,  at  each  end. 


228 


THE  VALVE  GEAR 


THE  VALVE  GEAR 


229 


g  a 


^^ 


^     /  ^^ 


11 


6:2 


In  many  cases 
the  eccentric  can- 
not be  placed  di- 
rectly in  line  with 
the  valve  stem  on 
account  of  the 
room  required  for 
the  main  bearing. 
To  provide  for  this 
the  eccentric  rod 
connection  is 
placed  between 
the  valve  and  the 
guide,  and  an  off- 
set pin  is  attached 
to  the  enlarged 
section  projecting 
out  to  the  line  of 
the  eccentric  rod 
as  shown  in  fig. 
407.  Here,  it  is 
necessary  to  make 
the  enlarged 
section  of  the 
valve  stem  square 
or  rectangular,  to 
prevent  the  stem 
turring  due  to  the 
angular  thrust  of 
the  eccentric  rod.* 
On  account  of  this 
turning  action,  it 
is  important  that 
there  he  no  lost 
motion  in  the  guide 
hearings. 


The  Guide.— 

The    object   of 
the    guide    is    to 


5ET  SCREW  \ 


6^ 


*N0TE.— In  this  type 
of  valve  stem,  the  square 
section  is  usually  a  sepa- 
rate part  with  a  threaded 
joint  A,  (figs.  402  and 
407),  to  facilitate  con- 
struction and  adjustment. 


230 


THE  VALVE  GEAR 


prevent  the  previously  mentioned  turning  motion,  and  any  side 
movement  of  the  valve  stem  which  may  occur  on  account  of 
the  action  of  the  eccentric  rod.  In  fig.  408,  the  guide  consists  of 
a  U  shaped  piece  attached  to  the  lower  end  of  the  steam  chest. 
This  style  is  used  extensively  on  marine  engines  when  the 
eccentric  is  directly  under  the  stem;  it  is,  however,  somewhat 
in  the  way  when  packing  the  stuffing  box. 


iiiiiiiii    liitmi 


Fig.  408. — Detail  of  marine  type  of  valve  stem  guide  with  adjustable  brasses. 


The  valve  stem  guide  shown  in  fig.  401  has  no  means  of  adjustment  for 
wear.  A  more  desirable  form  is  shown  in  fig.  408  having  a  box  with  ad- 
justable brasses;   this  is  the  regular  marine  type  as  used  on  large  engines. 

On  engines  having  offset  eccentrics,  there  are  usually  two  guides  which 
are  attached  to  the  engine  frame  as  shown  in  fig.  407. 

Two  projecting  arms  B,  C,  are  cast  to  the  frame  with  cross  pieces  D,  E, 
bolted  on,  and  serving  as  guides.  The  offset  pin  F  is  screwed  into  the 
square  section  of  the  stem  and  locked  by  a  nut. 

There  are  numerous  forms  of  guide  depending  on  the  design  of  the 
engine.  In  fig.  409  is  shown  the  guides  of  the  Brownell  engine.  Lubricating 
devices  are  attached  to  the  guides  and  below  is  a  tray  to  catch  the  waste  oil. 


THE  VALVE  GEAR 


231 


Rocker  Levers. — Sometimes  an  offset  pin  is  carried  on  two 
rocker  levers,  M,  and  S,  as  shown  in  fig.  410,  which  illustrates 
the  construction  used  on  the  American  Ball  engine. 


OFF  SET 


^ALVE  STEM  END  OFF  5ET  PIN 


OIL  TRAY 


Fig.  409. — ^Valve  stem  guides,  and  offset  pin  of  the  Brownell  engine.    The  figure  shows  also 
the  oihng  devices,  and  a  drain  tray  for  the  oil. 


ECCENTRIC  ROO 


Fig.  410. — The  American-Ball  engine.     View  showing  rock  shaft  C,  and  rocker  levers  M,  S, 
which  carry  the  offset  pin,  the  latter  being  attached  at  D  and  E. 


232 


THE  VALVE  GEAR 


The  pin  is  carried  by  two  rocker  levers  M,  and  S,  keyed  to  the 
shaft  C.  There  are  pivoted  joints  at  D,  and  E,  for  the  valve  stem 
and  eccentric  rod. 

In  operation,  the  rockers  move  through  a  small  arc,  and  a 
slight  up  and  down  movement  is  produced  owing  to  the  circular 
path  of  D.  The  stem  is  sufficiently  flexible  to  allow  for  this, 
hence  no  special  provision  is  made.  This  style  of  offset  pin  is 
used  to  advantage  on  engines  having  the  eccentric  rod  located 


Fig.  411. — Erie  City  high  speed  engine.  An  indirect  rocker  fulcrumed  at  A,  is  used  in  place 
of  an  offset  pin.  The  valve  stem  is  attached  at  B,  and  the  eccentric  rod  at  C.  To  allow  for 
side  motion  due  to  the  rocker,  a  flexible  joint  is  provided  at  S. 


outside  the  flywheel  where  the  offset,  or  distance  D  E,  is  con- 
siderable. 

Another  type  of  rocker  used  on  engines  of  this  class  consists  of  a  hori- 
zontal lever,  pivoted  near  the  center  as  shown  in  fig.  411. 

A  projection  M,  bolted  to  the  engine  frame  carries  the  lever  whose  ful- 
crum is  at  A,  connection  at  B,  being  made  with  the  valve  stem,  and  at  C, 
with  the  eccentric  rod.  Since  the  arm  A  B,  is  rather  small,  the  arc 
described  by  B,  will  cause  more  side  motion  of  the  stem  than  is  occasioned 
by  the  movement  of  D,  in  fig.  410,  hence  a  flexible  joint  is  provided  at  S, 
to  relieve  the  stem  of  undue  bending. 


THE  VALVE  GEAR 


233 


Oues.     What  is  a  direct  valve  gear? 

Ans.     One  in  which  the  valve  stem  and  eccentric  rod  move  in 
the  same  direction  as  shown  in  fig.  410. 

Oues.    What  is  an  indirect  valve  gear? 

Ans.     One  in  which  the  valve  stem  and  eccentric  rod  move 
in  opposite  directions  as  shown  in  fig.  411. 


Fig.  412. — "Vim"  horizontal  automatic  cut  off  engine  with  direct  valve  gear  without  rocker. 
The  eccentric  rod,  as  seen,  is  offset  with  pin  attached  to  a  wide  rectangular  valve  stem  end 
piece  workinig  in  two  bearings  to  prevent  lateralor  twisting  motion. 


The  Eccentric  Rod. — Motion  is  transmitted  from  the 
eccentric  to  the  valve  stem  or  rocker  by  the  eccentric  rod..  The 
rod  may  be  either  round  or  of  rectangular  section.  A  simple 
form  of  rod  is  shown  in  fig.  413  with  the  end  connections  in- 
dicated by  dotted  lines.  In  fig.  415  is  shown  a  rectangular  rod 
which  is  secured  to  the  strap  by  a  cross  piece  A,  and  stud  bolts 
B  and  C. 


234 


THE  VALVE  GEAR 


^— 


0- 

<: 


^1 


rt.o 


THE  VALVE  GEAR 


235 


Where  two  eccentrics  are  employed,  as  with  link  motion,  the  pin  end  is 
offset  as  shown  at  D,  fig.  414,  the  offsets  of  the  two  rods  being  on  opposite 
sides  to  permit  the  link  to  work  centrally.  The  pin  is  held  by  the  two 
jaws,  E  and  F. 

On  marine  beam  engines  the  eccentric  rods  are  of  great  length  and  to 
make  them  rigid  each  rod  is  usually  built  up  of  flat  wrought  iron  bars  in 
shape  of  a  tapering  lattice  girder.  The  extreme  end  is  a  solid  bar,  with  a 
notch  for  hooking  on  to  the  rocker  pin. 

A  pin  is  used  in  place  of  an  eccentric  on  many  high  speed  engines  where 
the  rod  is  located  outside  the  fly  wheel ;  the  rod  being  constructed  as  shown 
in  fig.  416.  Part  of  the  fly  wheel  and  the  rocker  are  indicated  in  dotted 
lines  to  show  the  position  of  the  rod. 


Fi:x  WHEEL 


ROCKER  PIN 


ECCENTRIC  PIN 


Fig.  416.— Outside  eccentric  rod  of  a  high  speed  engine.  With  rods  of  this  type,  an 
eccentric  pin  is  used  in  place  of  an  eccentric.  The  other  end  of  the  rod  is  usually  attached 
to  a  direct  rocker.    This  and  part  of  the  fly  wheel  are  shown  in  dotted  lines. 


The  Eccentric  and  Strap. — ^An  eccentric  is  the  equivalent 
of  a  crank  pin  which  is  so  large  in  diameter  that  it  embraces  the 
shaft  to  which  it  is  attached  and  dispenses  with  arms.  Its  object 
is  to  change  the  rotary  motion  of  the  shaft  into  a  reciprocating, 
or  to  and  fro  motion.  This  motion  is  transmitted  by  the  strap 
and  eccentric  rod  to  the  valve  stem  and  valve.  An  eccentric 
and  strap  of  simple  construction  is  shown  in  figs.  417  and  418. 

The  eccentric  E,  is  a  cast  iron  disc  having  a  projecting  boss  or  hub  H, 
containing  a  set  screw  I,  to  secure  it  in  any  position  on  the  shaft.     A,  is 


236 


THE  VALVE  GEAR 


the  center  of  the  ec- 
centric, and  O,  the 
center  of  the  shaft. 
The  hole  for  the 
shaft  is  drilled  out 
of  center  or 
"eccentric"  with  the 
center  of  the  disc, 
hence  the  name 
eccentric. 

The  distance  O  A 
between  the  center 
of  the  shaft  and  the 
center  of  the  eccen- 
tric is  the  eccentricity 
and  is  equal  to  one 
hcilf  the  throw.  This 
distance  is  sometimes 
wrongly  called  the 
throw. 


Throw 

Oues.  What  is 
the  throw  of  an 
eccentric? 

Ans.  Twice  the 
eccentricity  or  the 
amount  of  to  and 
fro  movement 
produced. 

The  throw  is  equal 
to  the  diameter  of 
the  circle  described 
by  the  center  of  the 
eccentric  as  it  re- 
volves around  the 
shaft.  Thus,  in  figs. 
417  and  418,  when 
the  center  of  the 
eccentric  is  at  A' 
and  the  end  of  the 


THE  VALVE  GEAR 


237 


rod  at  T',  the  end  of  the  rod  moves  from  T'  to  T"  as  the  center  of  the 
eccentric  moves  from  A'  to  A".  The  distance  T  T'  or  A'  A"  is  the  throw, 
some  erroneously  call  half  this  distance  the  throw. 

The  eccentric  is  embraced  by  a  strap  usually  made  in  two  pieces  D,  D'. 
These  are  held  together  by  the  bolts  M,  S,  liners  being  inserted  at  X  and  Y 
for  adjustment.  The  circumference  of  the  eccentric  is  recessed  at  J  and  K, 
to  register  with  a  groove  in  the  strap;  this  prevents  any  side  motion  of  the 
strap. 

The  eccentric  rod  is  attached  to  a  projection  or  neck  N,  usually  by  a 
threaded  conhection  as  shown.    At  W,  is  an  oil  well  for  lubrication. 

The  strap  is  recessed  at  F  and  G,  to  register  with  a  side  of  each  bolt  which 
prevents  the  latter  turning  when  the  nuts  are  tightened. 


ECCENTRICITY,  OR 
'A  THE  THROW. 


CRANK 


Figs  419  and  420. — Comparison  of  eccentric  and  crank.  An  eccentric  is  equivalent  to  a  small 
crank  whose  arm  O'  E'  is  equal  to  the  distance  O  E  between  the  center  of  the  shaft,  and  the 
center  of  the  eccentric.  This  distance  is  the  eccentricity,  or  one-tialf  the  throw.  Sometimes 
erroneously  called  the  throw. 

There  are  numerous  forms  of  eccentric,  the  one  shown  in  fig.  417  and  418 
serves  to  illustrate  the  principles  and  parts;  it  is  such  as  would  be  used 
on  a  small  horizontal  engine. 


Angular  Advance 


Oues.    What  is  the  angular  advance  of  an  eccentric? 

Ans.  The  number  of  degrees  the  eccentric  must  be  moved 
forward  from  a  position  at  right  angles  to  the  crank  to  give 
the  valve  its  linear  advance ^  that  is,  to  move  it  from  its  neutral 
position  to  its  position  when  the  crank  is  at  the  beginning  of 
the  stroke. 


238 


THE  VALVE  GEAR 


This  is  illustrated  in  figs.  421  and  422.  In  fig.  421,  the  crank  is  on  the 
dead  center  and  the  valve  in  its  neutral  position.  The  corresponding 
position  of  the  eccentric  is  shown  90  degrees  ahead  of  the  crank. 

When  the  crank  is  on  the  dead  center  the  valve  must  be  in  the  position 
-  shown  in  fig.  422,  a  distance  M  M',  to  the  right  equal  to  the  lap  plus  the  lead 
or  linear  advance.  Hence  the  eccentric  must  be  turned  ahead  on  the  shaft 
far  enough  to  move  the  valve  this  distance  from  its  neutral  position. 

To  find  the  angular  advance,  MM',  is  measured  off  to  the  right  of  the 
vertical  line  and  a  parallel  line  drawn.    This  cuts  the  path  of  the  eccentric 


NEUTRAL   POSITION    OF   VALVE 


LEAD 


PATH  OF  ECCENTRIC  CENTER 
Figs.  421  and  422. — Illustrating  linear,  and  angular  advance.  When  the  crank  is  on  the  dead 
center,  and  the  eccentric  set  90'-'  ahead,  the  valve  should  be  in  its  neutral  position  as  shown 
in  fig.  421.  The  valve,  however,  when  the  engine  is  on  the  dead  center,  must  be  at  a  distance 
(M  M',  fig.  422)  from  its  neutral  position  equal  to  the  lap  +  lead  or  in  its  position  of 
linear  advance.  The  eccentric  then  must  be  turned  ahead  through  an  angle  A  O  A',  its 
angular  advance,  sufficient  to  move  the  valve  to  its  linear  advance  position  M' . 

center  at  A',  from  which  it  is  evident  that  the  eccentric  must  be  turned 
ahead  through  the  arc  A  A',  to  move  the  valve  to  the  position  M',  A  O  A' 
being  the  angle  of  advance j  or  angular  advance  as  it  is  called. 


Oues.     What  objections  are  there  to  eccentrics? 


THE  VALVE  GEAR 


239 


Ans.  The  diameter  is  large  in  proportion  to  the  throw.  On 
account  of  this  large  diameter,  the  velocity  of  rubbing  against 
the  strap  is  considerable  as  compared  with  an  equivalent  crank 
pin.  This  causes  an  increase  of  friction  and  tendency  to  heat 
which  requires  closer  attention  to  be  given  to  lubrication  and 
adjustment  of  the  strap. 

Sometimes  the  eccentrics  on  small  engines  have  straps  with  only  a  single 
adjustment  as  shown  in  fig.  423. 

5TRAP  ADJUSTMENT 
ONE  PIECE  5TRAP 

ECCENTRIC 
ECCENTRIC  ROD 


Fig.  423. — Eccentric  strap  in  one  piece.  A  type  of  strap  for  use  in  inaccessible  places,  as  on 
small  multi-cylinder  marine  engines  having  cast  frames  and  valves  on  the  side.  On  account 
of  the  poor  fit  after  adjustment,  this  type  of  strap  is  liable  to  heat,  and  should  be  avoided 
in  design  wherever  possible. 

The  strap  is  one  piece  and  consists  of  a  split  ring  with  projecting  lugs  for 
the  adjusting  bolt.  Liners  may  be  inserted  in  the  space  between  the  lugs, 
or  a  set  screw  provided  to  hold  the  bolt  in  position. 

Eccentrics  of  this  type  are  regarded  by  some  (including  the  author)  as 
being  only  a  little  better  than  a  makeshift  because  when  wear  is  taken 
up  the  strap  looses  its  circular  form  and  no  longer  bears  properly  on  the 
eccentric,  making  it  more  liable  to  heat  in  operation. 


240 


THE  VALVE  GEAR 


Large  eccentrics  are  usually  made  in  two  unequal  parts  H  and 

H',  as  shown  in  fig.  424. 

These  are  held  together  by  the  key  bolts  M,  and  S;  the  keys  retain  them 
in  position  and  prevent  turning  when  the  nuts  are  tightened.  A  keyway 
K,  is  provided  to  retain  the  eccentric  in  position  on  the  shaft  and  also  a  set 


Fig.  424. — Eccentric  for  large  engines.     Usually  made  in  two  unequal  parts  H,  H',  and  held 
together  by  the  key  bolts  M,  S.    The  eccentric  is  retained  in  position  by  a  key  and  set  screw. 

screw  C.    The  larger  part  H,  of  the  eccentric  is  cast  with  ribs  (R,  R',  R'0> 
which  reduces  the  weight  and  provides  room  for  the  bolts  and  set  screw. 

An   eccentric  strap   having  micrometer   adjustment   as  used 
on  the  Ideal  engine  is  shown  in  figs.  425  to  428. 


THE  VALVE  GEAR 


241 


The  two  halves  of  the  strap  are  joined  at  the  bottom  by  a  construction 
possessing  the  elements  of  a  hinge.  At  the  top,  the  uniting  bolt  M,  passes 
through  a  sleeve  nut  S,  which  is  threaded  into  the  base  lug  L,  and  fixes  the 
distance  between  the  two  halves.  In  adjusting  the  strap,  the  nuts  M,  are 
slacked  and  the  sleeve  nut  S,  turned  to  regulate  the  distance  between  the 
two  halves,  and  the  nuts  M,  again  tightened  which  holds  the  two  halves 
rigidly  together. 


HIN&E  CONNECTIOH 


Figs.  425  to  428. — Eccentric  strap  of  the  Ideal  engine,  having  micrometer  adjustment.  Thi; 
two  halves  are  joined,  at  the  bottom  by  a  hinge  connection,  fig.  428,  and  at  the  top  by  a 
uniting  bolt  M,  fig.  426;  this  passes  through  a  sleeve  nut  S,  which  is  threaded  into  the  base 
lug  and  fixes  the  distance  between  the  two  halves. 


NOTE. — There  are  several  kinds  of  eccentric:  1,  the  circular,  or  eccentric  properly  so 
called,  and  2,  the  various  other  contrivances  bearing  the  name  of  eccentrics,  but  which  are 
virtually  cams,  such  as  the  heart  shaped  eccentric,  the  triangular  eccentric,  eccentrics  with 
a  uniformly  varied  motion,  etc. 

NOTE. — ^The  large  amount  of  friction  produced  between  the  eccentric  and  its  strap  renders 
the  application  of  the  eccentric  irnpracticable  in  cases  in  which  it  is  required  to  transmit  a 
great  force.  The  same  may  be  said  of  all  contrivances  bearing  the  name  of  eccentrics;  they 
are  applicable  only  when  the  force  to  be  transmitted  is  small. 

NOTE. — Because  of  the  relatively  high  velocity  of  the  rubbing  surface  as  compared  with 
an  eccentric  pin,  the  latter  is  the  more  desirable  and  is  used  in  best  practice  where  the  con- 
struction permits,  as  for  instance,  in  marine  engines  having  valves  on  the  side  operated  from  a 
valve  shaft. 

NOTE. — In  marint;  practice,  eccentric  rods  are  generally  made  of  steel  with  bushings 
at  the  top  ends,  and  the  eccentric  straps  are  generally  constructed  of  cast  steel  lined  with 
white  metal  as  bearing  surfaces,  the  eccentrics  being  of  cast  iron  or  cast  steel,  preferably  of 
the  former  metal  except  in  very  light  construction. 


242 


THE  VALVE  GEAR 


In  fig.  429  is  shown  the  strap  and  eccentric  rod  of  the  Erieco 
engine.  The  rod  is  attached  to  the  strap  at  A,  and  held  by  the 
set  screw  D. 


Fig.  429. — Erieco  eccentric  strap  and  rod.  The  strap  is  lined  with  Babbitt  metal,  and  the 
eccentric,  being  an  arc  which  properly  fits  the  strap,  makes  a  ball  and  socket  joint.  This 
arrangement  insures  cool  running  even  though  there  be  a  lateral  error  in  the  alignment. 

The  length  is  adjustable  by  means  of  the  threaded  end  E,  and  nut  B. 
Adjustment  for  the  bearing  is  made  at  C. 


NOTE. — Eccentric  Rod — The  diameter  of  the  eccentric  rod  in  the  body  and  at  the  eccen- 
tric end  may  be  calculated  in  the  same  way  as  that  of  the  connecting  rod,  the  length  being  taken 
from  center  of  strap  to  center  of  pin.  Diameter  at  the  link  end  =  .8  D  +  .2  in.  This  is  for 
wrought  iron.     Eccentric  rods  are  often  made  of  rectangular  section. 


VARIABLE  CUT  OFF  243 


CHAPTER  6 
VARIABLE  CUT   OFF 


Where  economy  of  steam  is  desirable,  engines  are  used  which 
automatically  adjust  themselves  to  any  change  in  the  load  by 
altering  the  cut  off.  These  are  called  automatic  cut  off  engines'^ 
as  distinguished  from  throttling  engines,  in  which  the  cut  off  is^ 
fixed  and  the  steam  supply  varied  at  the  throttle  valve.  In 
either  class  the  regulation  is  controlled  by  an  automatic  governor. 

There  are  several  methods  employed  to  vary  the  cut  off  as  by: 

1.  Shifting  eccentric ; 

2.  Swinging  eccentric  j  offset; 

3.  Rotating  eccentric  (independent  cut  off  valve); 

4.  Fixed  eccentric  (adjustable  lap  cut  off  valve) ; 

5.  So  called  expansion  valve  gears. f 

These   various   methods    may    be    divided   into   two    classes, 
according  as  the  cut  off  is  varied : 


*NOTE. — The  term  automatic  cut  off  engine  is  popularly  applied  to  that  large  class  of 
small  and  medium  sized  high  speed  engines  having  non- releasing  valve  gear;  broadly  speaking, 
any  type  of  engine  which  adjusts  itself  to  changes  in  load  by  automatically  varying  the  cut  off 
is  an  automatic  cut  off  engine. 

fNOTE. — The  au,thor  objects  to  the  term  "expansion  valve  gears,"  because  by  usage  it 
has  come  to  mean  single  variable  expansion  gears  as  distinguished  froni  fixed  expansion,  and 
double  gears,  all  gears  being  expansion  gears  except  a  few,  as  for  instance,  pump  gears, 
which  admit  steam  for  the  full  length  of  the  stroke 


244 


VARIABLE  CUT  OFF 


VARIABLE  CUT  OFF 


245 


1.  By  single  valve  gear,  or, 

2.  By  double  valve  gear. 

When  a  single  valve  gear  method  is  employed,  the  cut  off  is  called 
variable^  as  distinguished  from  the  methods  using  double  valve  gear,  in 
which  case  the  cut  off  is  said  to  be  independent. 

ANGULAR  ADVANCE 
.^       LATE  CUTOFF^ 


F\GS.  432  to  434. — Diagrams  showing  why  both  the  throw  and  angular  advance  must  be 
varied  to  change  the  cut  off.  In  the  figures  let  O ,  be  the  center  of  the  shaft,  and  E,  the  center 
of  the  eccentric  for  maximum  throw,  then  NOE,  is  the  angular  advance  for  maximum  throw. 
Now,  if  only  the  throw  be  changed  as  in  fig.  433,  the  center  of  the  eccentric  will  be  at  some 
point  E'  on  radius  OE;  evidently  this  reduces  the  linear  advance  LA,  to  L'A',  thus  dis- 
turbing the  lead.  Hence,  when  the  travel  is  changed,  as  by  reducing  the  eccentricity  from 
OE  to  OE',  figs.  432  and  433,  the  angular  advance  must  be  increased  from  NOE,  to  NOE", 
fig.  434,  in  amount  sufficient  to  maintain  the  linear  advance  constant  in  order  not  to  alter 
the  lead. 

Principles  of  Variable  Cut  Off  .—The  cut  off  of  the  ordinary 
slide  valve  may  be  altered  by  changing  both  the  throw  and 
angular  advance.  In  making  these  changes,  the  shorter  the 
travel,  the  earlier  the  cut  of.  This  way  of  changing  the  cut  off 
may  be  called  the  method  of  combined  variable  travel  and  variable 
angular  advance.  There  are  two  methods  of  moving  the  eccentric 
to  vary  both  the  travel  and  angular  advance: 


246 


VARIABLE  CUT  OFF 


1.  By  shifting; 

2.  By  swinging. 

To  distinguish  the  two  constructions,  the  first  is  called  the  shifting 
eccentric,  and  the  second  the  swinging  eccentric,  most  engines  being  fitted 
with  the  latter. 

The  Shifting  Eccentric. — The  principle  of  a  shifting  eccentric 
is  illustrated  in  fig.  435.    A  slot  S,  is  cut  in  the  eccentric  at  right 


LATE    CUT'OFF 
POSITION 


STRAIGHT  5L0T 
CRANK   PIN 


POSITION 


Fig.  435.— The  shifting  eccentric.  Two  arms  A,  B,  attached  to  the  eccentric,  pass  through 
the  bearings  C,  D.  The  eccentric  has  a  slot  S  to  permit  linear  movement  on  the  shaft. 
By  shifting  it  from  E  to  E',  the  throw  is  reduced,  and  the  angular  advance  increased,  the 
combined  effect  of  which  produces  an  earlier  cut  oflf.  There  is  considerable  movement  and 
friction  in  the  bearings  C,  D,  as  compared  with  the  swinging  eccentric.  The  lead  is  constant 
(not  considering  the  angularity  of  the  eccentric  rod). 

angles  to  the  crank;  two  arms  A,  B,  project  from  the  eccentric 
to  the  bearings,  C,  D,  which  are  attached  to  the  fly  wheel,  thus 
permitting  the  eccentric  to  ''shift"  at  right  angles  to  the  crank. 

For  a  late  cut  off  (full  gear),  the  position  of  the  eccentric  is  shown  in  full 


VARIABLE  CUT  OFF 


247 


lines  with  its  center  at  E.    In  this  position  O  M,  is  equal  to  the  eccentricity, 
or  half  the  throw,  and  N  O  E,  the  angle  of  advance. 

The  cut  off  is  shortened  by  reducing  the  throw  and  increasing  the  angular 
adiance.  This  is  done  by  shifting  the  eccentric  along  the  slot  to  some  inter- 
mediate position  as  that  shown  by  the  dotted  line::  with  center  at  E'.  This 
reduces  the  eccentricity,  or  half  throw  from  O  M,  to  O  M',  hence,  the  travel 
of  the  valve  has  been  reduced  twice  the  distance  MM',  and  the  cut  off 
shortened  an  amount  corresponding  with  the  increase  (E  O  E')  in  the 
angular  advance. 


Figs.  436  and  437. — Some  examples  of  shifting  eccentrics  as  used  on  traction  engines,  for  both 
variable  cut 'off  and  reverse.  Fig.  436,  Heilman  gear.  As  seen,  the  shifting  eccentric  slides 
in  V,  grooves,  being  geared  to  a  double  bell  crank,  which  is  connected  by  a  Imk  to  a  disc  and 
collar  arranged  to  slide  along  the  shaft.  A  second  bell  crank  and  rod  connects  the  collar  with  # 
the  control  lever.  Fig.  437  shows  the  Russell  variable  cut  off  and  reverse.  As  constructed, 
the  eccentric  is  made  to  shift  for  change  of  cut  off  or  reverse  by  a  single  bell  crank. 


248 


VARIABLE  CUT  OFF 


Since  the  center  of  the  eccentric  n^oves  in  a  line  E  E',  at  right  angles 
to  the  crank,  the  lead  remains  constant.*  The  angular  advance  increases 
as  the  cut  off  is  shortened.  In  moving  the  eccentric  from  E  to  E',  the 
angular  advance  increases  from  N  O  E  to  N  O  E'. 

Oues.  What  is  the  action  of  a  shifting  eccentric  in 
shortening  the  cut  off? 

Ans.  It  shortens  the  cut  off  by  reducing  the  throw  and  increas- 
ing the  angular  advance,  sufficiently  to  maintain  a  constant  linear 
advance,    {not  considering  the  eccentricity  of  the  eccentric  rod). 


SWING   CENTER 

EARLY  CUT  OFF 

Fig.  438. — The  swinging  eccentric.  The  arm  A,  is  pivoted  at  B,  in  line  with  the  shaft  and  crank  ■ 
pin.  This  location  of  the  swing  center  causes  the  lead  to  increase  as  the  cut  off  is  shortened. 
If  the  swing  center  be  located  on  the  opposite  side  at  B',  the  lead  will  decrease  as  the  cut  off 
is  shortened. 


The  Swinging  Eccentric. — The  chief  objection  to  the  shifting 
eccentric  is  the  friction  brought  on  the  bearings  (C,  D,  fig.  435) 
which  is  Hable  to  interfere  with  the  free  movement  of  the  eccen- 
tric, and  thus  reduce  the  sensitiveness  of  the  governor,  especially 

*N0TE. — The  effect  of  the  angularity  of  the  eccentric  rod  is  to  diminish  the  lead  as 
^the  eccentric  moves  from  E  to  E',  but  since  the  rod  is  very  long  in  proportion  to  the  throw, 
the  lead  is  only  slightly  reduced,  hence  for  simplicity  the  angularity  is  neglected  in  the  ex- 
planation. 


VARIABLE  CUT  OFF 


249 


on  account  of  the  difficulty  of  lubricating  a  bearing  rotating 
around  a  center,  accordingly  the  shifting  eccentric  is  better 
adapted  for  an  adjustable  or  non-automatic  cut  off  engine.* 

To  overcome  this  defect,  the  swinging  eccentric  has  been  devised  by 
means  of  which  the  considerable  Hnear  motion  through  the  bearings 
(C,  D,  fig.  435)  has  been  reduced  to  a  very  small  circular  motion. 


Fig.  439. — Fly  wheel  and  governor  of  Buffalo  engine  illustrating  the  swinging  eccentric.  It 
should  be  noted  that  in  the  design  here  illustrated  the  swing  center  is  near  the  radial  slot 
instead  of  at  the  end  of  the  arm  as  in  fig.  438. 


A  swinging  eccentric  has  one  arm  A,  fig.  438,  of  any  convenient  length, 
and  pivoted  at  some  point  as  B,  on  a  line  joining  the  shaft  and  crank  pin 
centers.  The  point  B,  is  called  the  swing  center.  A  circular  slot  S,  is  cut  in 
the  eccentric,  having  sides  in  the  form  of  arcs  of  circles  described  with 
B,  as  center. 


*N0TE. — Owing  to  the  centrifugal  force  thus  set  up,  the  oil  will  not  remain  long  in  the 
bearing  but  is  thrown  off  at  the  outer  ends. 


250 


VARIABLE  cur  OFF 


The  action  is  similar  to  that  of  the  shifting  eccentric,  that  is,  the  cut  off 
is  shortened  by  a  reduction  of  throw  and  an  increase  of  angular  advance. 
This  is  done  by  swinging  the  eccentric  about  the  swing  center  B,  from  its 
full  gear  position  E,  to  some  intermediate  position  E'.  Here,  the  angular 
advance  has  increased  from  N  O  E,  to  NO  E',  and  the  throw  reduced  by 
twice  the  distance  M'M. 

Oues.  What  is  the  action  of  the  swinging  eccentric 
in  shortening  the  cut  off? 

Ans.  It  shortens  the  cut  off  hy  reducing  the  throw  and'  increas- 
ing the  angular  advance  in  such  proportion  as  to  give  an  increasing 
lead, 

RADIAL  SLOT 
LATE    CUT  OFF 

SWING    CENTER 

CRANK    PIN 

\ 


EARLY    CUT  OFF 


Fig.  440. — The  offse    swinging  eccentric.    With  the  swing  center  located  as  in  the  figure, 
the  lead  is  the  same  for  maximum  and  minimum  cut  off  and  greatest  in  mid  position. 

It  should  be  noted  in  fig.  438,  that  as  the  center  of  the  eccentric  is  moved 
from  E  to  E',  to  shorten  the  cut  off,  the  lead  is  increased  an  amount  equal 
to  the  distance  L*. 

Ques.  How  would  the  action  of  the  swinging  eccentric 
be  modified  if  the  swing  center  be  located  on  that  side  of 
the  shaft  opposite  the  crank  pin? 

Ans.     The  lead  would  decrease  as  the  cut  off  is  shortened. 


*NOTE. — Taking  into  account  the  angularity  of  the  eccentric  rod,  the  actual  increase 
in  the  lead  is  slightly  less  than  the  distance  L. 


VARIABLE  CUT  OFF 


251 


This  is  objectionable  in  that  it  reduces  the  port  opening  as  the  cut  off  is 
shortened,  thus  producing  wire  drawing  which  lowers  the  admission  pressure. 


The  Ofifset  Swinging  Eccentric. — On  some  engines  the 
swinging  eccentric  is  located  with  its  swing  center  offset  from  the 
line  joining  the  shaft  and  crank  pin  centers  as  shown  in  fig.  440. 


Fig.  441.— Valve  gear  of  the 
Lentz  poppet  valve  engine, 
illustrating  the  shifting  type 
eccentric.  In  this  eccentnc, 
the  shifting  slot  is  cut  straight, 
the  axis  of  the  slot  making 
with  the  line  joins  the  center 
of  the  shaft  and  center  of  the 
eccentric,  an  angle  equal  to 
the  angular  advance,  the 
eccentric  axis  being  in  advance  of  the  slot  axis.  The  effect  of  straight  slot  eccentric  wh«n 
used  for  variable  cut  off  is  to  give  a  constant  lead  for  all  degrees  of  expansion  (not  con- 
sidering the  angularity  of  the  eccentric  rod) . 


Ques.    What  is  the  object  of  offsetting  the  swing  center? 

Ans.  To  compromise  between  the  conditions  described  in 
the  last  two  examples,  that  is,  instead  of  an  increasing  or  de- 
creasing lead,  by  offsetting  the  swing  center  the  same  lead  is 
obtained  at  both  maximum  and  minimum  cut  off  with  a  somewhat 
larger  lead  in  mid  position. 


252 


VARIABLE  CUT  OFF 


In  fig.  440,  the  swing  center  B,  is  offset  above  the  crank  axis  one-half  the 
distance  from  E,  to  this  axis.  This  position  B,  gives  the  same  lead  in  the 
two  extreme  positions,  and  it  should  be  noted  that  the  total  increase  of 
lead  L,  is  only  one-half  the  increase  L,  of  fig.  438.  The  two  positions  illus- 
trated, correspond  to  those  of  the  two  preceding  figures  showing  the  same 
angles  of  advance  but  less  increase  of  lead.  From  the  figure  it  is  seen 
that  if  the  eccentric  be  moved  to  the  extreme  position  E",  the  lead  will 
decrease  and  become  equal  to  the  original  amount  for  the  full  gear 
position  E. 


Pig.  442. — ^Leffel  adjustable  shifting  eccentric.  It  consists  of  a  hub  plate  keyed  to  shaft  with 
valve  eccentric  bolted  thereto,  in  a  manner  enabling  adjustment  of  the  cut  off  up  to  three- 
fourth  stroke,  or  reversing  motion  of  engine  with  same  range  of  cut  off. 


Owes.  What  is  the  action  of  the  offset  swinging  eccen- 
tric in  shortening  the  cut  off? 

Ans.  It  shortens  the  cut  of?  by  reducing  the  throw  and  increas- 
ing the  angular  advance,  in  such  proportion  that  the  lead  increases 
for  full  gear  to  mid  position  and  then  decreases  to  the  original 
amount  at  minimum  cut  of,  the  total  increase  being  less  than 
that  produced  by.  the  swinging  eccentric. 


VARIABLE  CUT  OFF 


253 


Independent  Cut  Off. — For  maximum  economy,  a  much 
earlier  cut  off  is  required  than  that  produced  by  a  sUde  valve  in 
full  gear.  For  instance,  a  single  cylinder  engine  to  run  with  the 
least  steam  consumption  per  horse  power .  must  cut  off  from 
one-third  to  one-fifth  when  running  non-condensing  and  from 
one-fifth  to  one-seventh  when  running  condensing,  the  particular 
point  depending  upon  the  pressure  and  quality  of  the  steam,  etc. 


ECCENTRIC 


SWING 
CENTER 


CENTER  OF 
SHAFT 


Fig.  443. — ^Wheel  end  of  American  Ball  automatic  cut  off  engine  showing  eccentric  pin,  largely 
used  in  place  of  an  eccentric.    The  arms  and  spring  are  parts  of  the  governor. 


A  considerable  range  of  cut  off  is  required  on  account  of 
variations  in  power  demands. 

The  plain  slide  valve  is  designed  for  the  latest  cut  off  required 
and  with  a  movable  eccentric  the  valve  is  made  to  cut  off  shorter 


254 


VARIABLE  CUT  OFF 


INCREASE  IN  ANGULAR  ADVANCE /^^ 


ECCENTRIC  AT  END  OF  THROW  - 
BEFORE  PORT.  15  FULLY  OPENED 


i.    Slow  and  insufficient  opening  of  the  port  for  admission 

THROW  FOR  LATE  CUT  OFF    };rj 
THROW  FOR  EARLY  CUT  OFF 


2.    Pre-release  occurs  too  early 


LINEAR  DISPLACEMENT  CAUSING-^ 
PREMATURE  COMPRESSION  X 


% 


3.    Compression  begins  too  early 

Figs.  444  to  446. — Defects  of  the  slide  valve  at  early  cut  off:  1,  fig.  444 ,  slow  and  insufficient 
Port  opening.  Note  that  the  eccentric  center  E',  is  at  the  end  of  its  throw;  hence  the  valve 
movement  in  opening  the  port  is  comparatively  slow;  2,  fig.  445,  pre-release  occurs  too  early. 
This  is  due  to  the  increased  angular  advance  displacing  the  valve  to  the  left  by  the  distance 
AB;  3,  fig.  446,  compression  begins  too  early.  Similarly  as  in  2,  the  increased  angular 
advance  displaces  the  valve  to  right  by  the  distance  A'B',  causing  the  valve  to  close  to 
exhaust  too  soon.  In  the  figures,  E,  is  the  center  of  the  eccentric  for  full  gear  or  late  cut  off, 
and  E',  for  early  cut  off. 


VARIABLE  CUT  OFF 


255 


as  previously  explained.  This  combination  has  the  advantage 
of  simplicity  but  for  very  early  cut  offs  it  possesses  certain 
defects  which  become  more  pronounced  with  the  shortening 
of  the  cut  off.     These  defects  are,  briefly: 

1.  Slow  and  insufficient  opening  of  the  port  for  admission. 


LATE  CUT  OFF 

[*HNCREA5E  IN  LEAD  (EARLY  CUT  OFF) 
NORMAL  LEAD  (lATE  CUT  OFF) 


CAU5E  OF 
.'INCREASE  IN  LEAD 


EARLY  CUT  OFF 


SWING  CENTER 


Figs.  447  and  448. — Defects  of  the  slide  valve  at  early  cut  off:  4,  lead  not  constant  with  swinging 
eccentric.  Case  I,  Swing  center  between  shaft  and  crank  pin.  For  early  cut  off,  the  center 
E,  of  the  eccentric  swings  through  the  arc  EE',  fig.  448,  to  position  E',  thus  increasing  the 
angular  advance  and  reducing  the  travel,  but  in  so  doing,  the  valve  is  displaced  to  the  right 
a  distance  AB,  increasing  the  lead  by  this  amount. 

On  account  of  the  reduced  travel,  the  valve  moves  slower  at  admission 
and  cut  off;  this  causes  wire  drawing  at  these  points  which  together  with 
insufficient  port  opening  due  to  the  small  travel  results  in  a  loss  of  pressure. 


2.  Pre-release  occurs  too  soon. 

Since  the  valve  opens  to  exhaust  sooner  than  is  necessary,  the  full  benefit 
which  might  be  derived  from  expansion  of  the  steam  is  not  realized. 


256 


VARIABLE  CUT  OFF 


3.  Compression  begins  too  early.  * 

This  produces  a  resistance  in  excess  of  that  required  to  overcome  the 
momentum  of  the  reciprocating  parts.  The  slower  the  engine  speed,  the 
more  pronounced  is  this  effect. 


SWING 

SWING  CENTER 


Figs.  449  and  450. — Defects  of  the  slide  valve  at  early  cut  off;  5,  lead  not  constant  with 
swinging  eccentric.  Case  H,  swing  center  and  crank  pin  on  opposite  sides  of  shaft.  When 
the  center  of  the  eccentric  swings  through  the  arc  EE',  fig.  450,  to  shorten  the  cut  off,  the 
valve  is  displaced  to  the  left  a  distance  AB,  thus  decreasing  the  lead -by  this  amount. 


4.  The  lead  is  not  constant  (^with  swinging  eccentric).  The 
variation  of  lead  is  influenced  chiefly  by  the  position  of  the 
swing  center,  and  also  by  the  length  of  the  swing  radius. 

The  independent  cut  off  is  intended  to  overcome  these  defects 
and  consists  of: 


VARIABLE  CUT  OFF 


257 


1.  A  main  valve  which  controls  the  points  of  admission  release 
and  compression,  and 

2.  A  cut  off  valve  which  controls  the  cut  off. 

There  are  two  eccentrics,  one  for  each  valve.  The  main  valve  is  operated 
by  a  fixed  eccentric,  and  the  cut  off  valve  by  a  rotating  eccentric.  With 
this  combination,  the  cut  off  may  be  varied  without  changing  the  positions 
of  release  and  compression. 

Oues.    Where  is  the  cut  ofif  valve  located? 


Fig.  451. — The  Gonzenbach  independent  cut  off  valve.  This  is  located  in  a  separate  steaitt 
chest  above  the  main  valve,  the  latter  being  an  ordinary  slide  valve  which  controls  the 
steam  distribution  with  the  exception  of  cut  off.  The  range  of  cut  off  is  limited,  and  the 
lower  steam  chest  presents  a  large  clearance  which  is  objectionable.  Moreover,  the  main 
valve  is  inaccessible. 


Ans.     It  may  be,  1,  placed  in  a  separate  steam  chest,  or  2, 
arranged  to  work  on  the  back  of  the  main  valve. 

Oues.     What  is  it  called  when  arranged  to  work  on  the 
back  of  the  main  valve? 

Ans.     A  riding  cut  off. 

Oues.    Describe  the  type  with  separate  steam  chest* 


258 


VARIABLE  CUT  OFF 


Ans.  The  Gonzenbach  valve  shown  in  fig.  451  is  an  example 
of  this  type.  In  the  figure,  the  main  valve,  which  is  the  lower, 
is  an  ordinary  slide  valve;  the  cut  off  valve  which  works  on  a 
ported  partition  directly  above,  is  of  the  gridiron  type,  that  is, 
there  are  a  number  of  steam  ports  (A,  B,  C,)  in  order  to  secure 
.a  quick  cut  off  with  moderate  travel. 

During  admission,   steam  passes  through  the  ports  A,  B,  C,  into  the 
lower  steam  chest  and  to  the  cylinder  through  either  one  of  the  cylinder 

-NEGATIVE  LAP 


Fig.  452,- 


STEAM   PORTS- 

-Gonzenbach  cut  off  valve  in  neutral  position  showing  negative  lap. 


ports  which  happens  to  be  open.  The  action  of  the  cut  off  valve  differs 
from  the  ordinary  valve  in  that  while  the  latter  opens  and  closes  the  port 
with  the  same  edge,  the  cut  off  valve  does  this  with  the  two  edges,  that 
is,  the  port  in  the  valve  passes  bodily  across  the  port  in  the  seat. 

Oues.     How  is  the  cut  oflf  varied? 


NOTE. — If  the  travel  of  the  valves  on  a  lodomotive  for  full  gear  be  414  to  5  inches,  for  a 
lead  of  i^  inch  at  full  gear,  and  ^e  inch  at  mid-gear,  a  steam  lap  of  %  inch  and  no  exhaust  lap 
will  secure  excellent  results;  but  if  the  engine  were  never  to  run  at  a  speed  of  over  20  miles 
an  hour,  an  exhaust  lap  of  }4  inch  could  be  used  to  advantage.  Most  builders  of  stationary 
engines  give  so  much  exhaust  lap  that  a  considerable  back  pressure  is  caused,  and  the 
engines  can  not  be  run  at  high  speed,  and  for  two  reasons:  1st,  that  this  steam* does  not  get 
ooit  of  the  cylinder  fast  enough,  and,  2nd,  there  is  not  enough  cushion  to  take  up  the  momentum 
of  the  connections  at  high  speed.  An  early  release  and  strong  cushion  are  required  for  high 
speeds.  At  moderate  speed  an  early  release  and  strong  cushion  deaden  the  motion  of  the 
engine  over  the  centers,  and  the  use  of  two  slide  valves,  one  on  top  of  the  other,  was  suggested 
by  Meyer.  A  false  valve  seat  was  suggested  by  Rankine,  with  the  object  of  obtaining  a  quicker 
cot  off,  the  seat  being  moved  by  one  eccentric  while  the  valve  was  moved  by  another.  In 
this  way  the  effect  of  an  eccentric  w  ith  greater  throw  was  obtained.  The  first  change  suggested 
by  Gonzenbach  consisted  in  making  the  steam  chest  in  two  chambers.  In  the  one  next  the 
cylinder,  the  ordinary  slide  was  employed  while  the  steam  came  in  through  openings  from  the 
other  cham.ber,  these  openings  were  covered  by  a  simple  slide  moved  by  an  eccentric.  Thus 
the  inlet  and  exhaust  were  regulated  by  the  ordinary  slide,  but  the  second  one  cut  off  the  sup- 
fily  of  steam.  As  the  principal  objection  to  this  was  the  large  clearance  space  left  in  the  main 
steam  chest  and  the  consequent  waste  of  steam,  the  Meyer  gear  became  the  favorite. 


VARIABLE  CUT  OFF 


259 


Ans.     By  turning  the  cut  off  valve  eccentric  forward  or  back- 
ward on  the  shaft  as  the  case  may  be.* 

Fig.  452  vshows  the  cut  off  valve  in  its  neutral  position  from  which  it  is  seen 
that  the  valve  has  negative  lap.  This  may  equal  or  exceed  the  width  of 
the  ports  in  the  seat;  the  negative  lap  being  the  distance  A,  measured 
from  one  edge  of  the  seat  port  to  the  opposite  edge  of  the  valve  port. 


The  principles  of  the  Gonzenbach  valve  are  best  understood 
by  the  application  of  the  Bilgram  diagram. 


Fig.  453. — Rider  variable  cut  off  gear.  In  this  riding  cut  off  gear,  the  cut  off  is  altered,  as  in 
the  Meyer  gear  by  varying  the  lap.  In  construction,  the  back  of  the  main  valve  is  hol- 
lowed into  a  part  of  a  cylinder  whose  axis  is  the  center  of  the  riding  valve.  The  lap  edges 
of  the  riding  valve  and  steam  edges  of  the  main  valve  are  tapered  in  such  a  manner  that  by 
rotating  the  riding  valve,  its  lap  is  changed.  This  rotation  is  accomplished  by  a  spindle 
attached  to  the  governor,  gearing  into  a  sector  on  the  valve  stem. 

Problem. — In  a  Gonzenbach  valve  gear  the  main  valve  has  }/(q  lead; 
J/^  inch  port  opening,  and  cuts  off  at  ^/lo  stroke;  the  cut  off  valve  has 
3  ports  giving  3^  inch  port  opening  each.  Required  the  negative  lap  and 
positions  of  the  cut  off  valve  eccentric  for  the  earHest  and  latest  cut  off. 


*N0TE. — The  effect  of  this  is  to  change  the  angular  advance  which  alters  the  cut  off. 
The  expansion  eccentric,  unlike  the  shifting  or  swinging  eccentric,  does  not  reduce  the  travel 
in  changing  the  cut  off. 


260 


VARIABLE  CUT  OFF 


In  fig.  454  crank  position  C,  for  latest  cut  off,  the  center  Em,  of  the 
main  eccentric,  and  lap  of  the  main  valve  are  found  in  the  usual  way. 

The  lead  position  is  now  found  by  drawing  the  line  LL',  through  O,  and 
tangent  to  the  main  valve  lap  circle. 

At  the  latest  cut  off  (^/lo  stroke),  the  negative  lap  circle  must  be 
tangent  to  the  line  OC,  and  also  tangent  to  the  lead  position  OL. 


VAt,\/£S    IN  LEAD   POSITION 


Fig.  454. — Application  of  the  Bilgram  diagram  to  the  Gonzenbach  independent  cut  off  gear. 
The  relative  positions  of  the  valves  and  eccentrics  are  shown  for  four  crank  positions  which 
illustrates  the  operation  of  the  gear. 


Since  the  cut  off  valve  has  three  ports,  it  is  equivalent  to  a  single  valve 
having  three  times  the  port  opening  and  travel.  Hence,  with  radius  of  IJ^ 
inch  equal  to  three  times  the  port  opening  of  each  port  of  the  cut  off  valve, 
describe  the  negative  lap  circle  tangent  to  OC  and  OL,  which  gives  the 
position  Q',  of  the  cut  off,  valve  eccentric  for  latest  cut  off. 

Starting  at  crank  position  A,  and  with  the  cut  off  eccentric  at  Q',  both 
valves  are  open  to  lead;  the  main  valve  is  at  a  distance  QB,  from  its  neutral 


VARIABLE  CUT  OFF  261 


position,  and  the  cut  off  valve  at  a  distance  Q'B'.  This  latter  distance 
being  less  than  the  negative  lap,  the  cut  off  ports  are  open  an  amount 
B'M  equal  to.  the  lead. 

As  the  crank  moves,  the  cut  off  ports  are  further  opened,  up  to  position 
C,  where  they  stand  wide  open  as  shown,  this  being  the  neutral  position 
for  the  cut  off  valve. 

As  the  crank  advances  further,  the  cut  off  begins  to  close  the  port,  not 
by  changing  its  direction  as  in  the  case  of  the  slide  valve  but  by  continuing 
its  movement  to  the  end  of  its  travel.     Cut  off  occurs  at  crank  position  C. 

The  earliest  point  of  cut  off  is  determined  by  extending  CO,  downward 
and  finding  Q",  such  as  to  make  the  negative  lap  circle  tangent  to  CO, 
extended,  and  drawing  OC",  tangent  to  the  negative  lap  circle  which  gives 
the  crank  position  for  earliest  cut  off.  After  passing  this  point  expansion 
takes  place  both  in  the  cylinder  and  the  lower  steam  chest  until  the  main 
valve  cuts  off  at  position  OC,  where  it  is  continued  in  the  cylinder  alone 
until  pre-release. 

Ques.    Mention  the  defects  of  the  Gonzenbach  valve. 

Ans.  In  shortening  the  cut  off  with  this  valve  gear  admission 
to  the  lower  steam  chest  occurs  earlier  and  earlier,  hence  there  is 
a  point  beyond  which  the  cut  off  valve  would  admit  steam  to  the 
lower  steam  chest  before  the  main  valve  had  closed  its  port  ta  . 
admission  in  the  previous  stroke,  thus  admitting  steam  to  the 
cylinder  twice  during  the  stroke. 

Thus  in  fig.  454,  if  the  cut  off  eccentric  be  advanced  to  Q"\  the  negative 
lap  circle  will  cut  OC,  extended,  indicating  that  the  cut  off  valve  ports  were 
open  a  distance  RS,  when  the  main  valve  closed  on  the  previous  stroke^ 
thus  readmitting  steam  to  the  cylinder  from  crank  positions  Cs,  to  Cr, 
during  the  expansion  period  of  the  previous  stroke. 

This  limits  the  range  of  cut  off,  and  in  order  to  secure  an  earlier  cut  off,  it  is 
necessary  to  design  the  main  valve  for  shorter  cut  off.  The  range  of  cut  off 
is  therefore  limited.  Moreover,  on  account  of  the  large  clearance  of  the 
lower  steam  chest,  the  full  expansion  due  to  the  cut  off  is  not  secured,  the 
difference  between  the  apparent  and  real  expansion  increasing  for  early 
cut  offs.     An  additional  defect  is  that  the  main  valve  is  inaccessible. 

The  Gonzenbach  valve,  on  account  of  these  objections  is  not 
extensively  used,  however,  it  serves  to  make  cleg,r  the  general 
principles  of  independent  cut  off. 


252 


VARIABLE  CUT  OFF 


The  Riding  Cut  Off. — The  large  clearance  and  inaccessible 
main  valve  of  the  Gonzenbach  gear  are  overcome  in  the  riding 
cut  off  by  placing  both  valves  in  one  steam  chest  and  using  the 
back  of  the  main  valve  as  a  seat  for  the  cut  off  valve,  that  is, 
the  cut  off  valve  ''rides"  on  the  main  valve,  hence  the  name 
riding  cut  df. 

NEC.  LAP 


STEAM    EDGE 


RIDING 


CUT  OFF 
STEAM 


PASSAGE 


MAIN    VALVE 


Fig.  455. — ^Riding  cut  off  valve  with  outside  cut  off  edges.  In  operation  the  cut  off  valve 
travels  or  "rides"  on  top  of  main  valve,  and  with  fixed  lap  as  above,  receives  its  movement  1, 
from  a  rotating  eccentric,  that  is,  an  eccentric  loosely  journalled  on  the  shaft  so  that  its 
angular  advance  may  be  changed  to  vary  the  cut  off,  under  control  of:  1,  a  governor,  or  2, 
a  fixed  eccentric  with  link  motion.  The  riding  cutoff  valve  with  outside  cut  off  edges  gives 
quickest  cut  off  with  early  cut  offs . 


STEAM 
ETDGE 


Fig.  456. — Riding  cut  off  valve  with  inside  cut  off  edges.    This  arrangement  having  inside  cut 
<iff  edges  gives  quickest  cut  off  with  late  cut  offs. 

Fig.  455  shows  a  simple  form  of  riding  cut  off.  Both  valves  are  shown 
in  neutral  position,  in  order  to  show  the  positive  lap  of  the  main  valve,  and 
negative  lap  of  the  cut  off  valve. 

The  main  valve  is  nothing  more  than  the  ordinary  slide  valve  having 
steam  passages  in  the  end  leading  to  the  back  which  is  machined  to  form 
the  seat  for  the  cut  off  valve. 

Fig.  456  sho^s  a  riding  cut  off  valve  which  cuts  off  at  the  inside  edges 
of  the  ports;   it  necessarily  has  considerable  positive  lap. 


VARIABLE  CUT  OFF 


263 


Methods  of  Variable  Cut 
Off   with   Riding  Valve.— 

Cut  off  by  a  riding  valve  may 
be  varied  in  three  ways, 
as  by: 

1.  Variable     angular     ad- 

vance; 

2.  Variable  lap; 

3.  Variable  travel. 

The  first  method  employs  a 
rotating,  or  loosely  journaled 
eccentric  for  the  cut  off  valve 
whose  angular  advance  is  con- 
trolled by  a  governor. 

The  second  method  has  a 
fixed  eccentric  to  operate  the  cut 
off  or  "riding"  valve,  the  lap  of 
the  latter  being  adjustable  by  a. 
right  and  left  screw. 

The  third  method  employs  a 
link  to  vary  the  travel  of  the 
riding  valve. 

For  convenience,  the  eccentric 
which  operates  the  riding  valve 
is  called  the  riding  eccentric* ;  it  is 
called  by  some  writers  the  cut 
off  eccentric,  and  more  commonly, 
though  ill  advisedly,  the  ex- 
pansion eccentric. 

1.  Riding   Cut   Off;  Va« 
riable  Angular  Advance. — 

The  usual  range  of  angular 
advance  given  to  the  riding 


,;  C  a»  rt  S 
O  rt  w  1-1  rt 


*NOTE. — The  term  riding  eccentric  is 
used  for  the  loosely  journaled  eccentric 
connected  to  the  riding  valve  to  distinguish 
it  from  the  fixed  or  main  eccentric  which, 
operates  the  main  valve.  The  symbols  Br- 
and Em  being  used  to  respectively  desig- 
nate each. 


264 


VARIABLE  CUT  OFF 


eccentric  is  from  a  little  less  than  90°  up  to  180°.  The  relative 
positions  of  the  two  eccentrics  are  such  that  the  valves  move  in 
opposite  directions  at  cut  off  (within  limits)  for  a  well  designed 
gear.  I 

The  following  example  will  serve  to  illustrate  the  features  of 
this  gear. 

V 

VS  CUTOFF  ^^- ~^^ 

V8  CUT  OFF 

F 


Pig.  458. — Method  of  transferring  crank  positions  determined  for  given  cut  off.  In  order  not 
to  complicate  the  Bilgram  diagram  all  unnecessary  lines  should  be  omitted,  hence  the  crank 
positions  for  given  cut  offs  are  best  determined  in  a  separate  diagram  as  in  fig.  457  and  then 
transferred,  as  above.  In  the  figure  draw  a  horizontal  line,  and  with  radius  =  0  D,  of  fig.  457, 
describe  the  semi-circle  D  E  F  G.  With  D,  as  center,  and  radius  =  distance  D  to  E,  of  fig.  457 
describe  an  arc  cutting  the  semi-circle  at  E,  giving  crank  position  O  E,  for  Vo  cut  off.  A 
similar  construction  gives  O  F,  crank  position  for  H  cut  off.  After  locating  O  E  and  O  F,  the 
semi-circle  and  radii  D  E  and  G  F,  should  be  erased  leaving  only  the  horizontal  line  and  the 
two  cut  off  positions  O  E  and  O  F,  to  be  used  in  the  Bilgram  diagram  fig.  459. 


e:'/5C,o 


F^/fiC.O 


PORT  OPENING  ARC 


Scale:  full  size 


Fig.  459.— Bilgram  diagram  for  main  valve.     Here  the  lap,  angular  advance,  and  travel  are 
determined  for  J^  cut  off  and  ^  port  opening  as  explained  in  the  accompanying  text. 


VARIABLE  CUT  OFF 


265 


Example. — Determine  the  dimensions  of  a  riding  cut  off  that  will  meet 
the  following  requirements:  maximum  cut  off  %  stroke;  lead  ^6  in.; 
ports,  ^i  in. ;  port  opening  not  less  than  3^  in.  for  any  cut  off  up  to  Vs 
stroke.    Bridges  ^2  in. ;  connecting  rod  ratio  23^  :  1. 

1.  Find  crank  position  for  Vs  and  J4  stroke  as  in  fig.  457; 

2,  Transfer  the  crank  positions  for  \^  and  ]4  cut  off  just  found  to  fig.  459, 
as  explained  in  fig.  458; 

Cm  0  Cr 
NEUTRAL     T    POSITION 


STEAM  EDGE 
STEAM   PASSAGE 

I'       H 


EXTREME 
POSITION 


Scale:  half  size 

Pigs.  460  and  461. — Detail  of  main  valve  and  seat.  On  A  B,  lay  off  the  steam  port  C  E== 
M  in.,  the  port  opening  C  D=^A  in.,  and  the  bridge  E  F  =  H  in.  Sketch  in  valve  end  in 
extreme  position.  D,  will  be  the  steam  edge.  Lay  off  D  H  =  ^  in.  and  draw  D  D',  and 
H  H',  giving  the  steam  passage  through  the  valve.  This  is  usually  made  same  size  as  the 
port  to  reduce  friction.  I  F,  the  end  of  the  valve  is  located  far  enough  beyond  H  H',  to  give 
a  steam  tight  joint,  say  }4  in.  Locate  G,  the  exhaust  edge  of  the  valve,  so  that  D  G  =  lap  + 
port  =%  in.  +^  in.  The  edge  G',  of  the  bridge  is  so  located  that  G  G'  =  C  E.  The  center 
line  O  O,  is  now  drawn  half  way  between  P  and  G'.  Transfer  the  detail  of  valve  end  thus 
found  to  A'  B',  showing  it  in  neutral  position,  and  complete  the  valve  and  seat  as  shown. 

3,  Find  outside  lap  and  travel  of  main  valve  for  He  lead,  J/g  cut  off,  and  a 
trial  port  opening  of  say,  ^  in ; 

In  fig.  459  draw  the   lead  line  Vie  in.  above,  and    parallel    to  the  horizontal  line. 
With  radius  O  B  =^  in.  port  opening,  describe  the  port  opening  arc  B  D. 


NOTE. — In  this  chapter,  O  0,=center  line  of  valve  seat;  Cm=center  line  of  main  valve; 
Cr=center  Hne  of  riding  valve;  Em=center  of  main  eccentric;  Er=center  of  riding  eccentric; 
Ev  =center  of  virtual  eccentric. 


266 


VARIABLE  CUT  OFF 


>  «>  S^  1^  «^ 

^•^rc;  c  ^  <u 
w  o  o  <u.i2'^ 


Describe,  with  a  center  Q, 
and  radius  found  by  trial  the 
lap  circle  tangent  to  cut  off 
line  O  F,  lead  line  and  port 
opening  arc  B  D.  Q  L,  then 
=  outside  lap,  and  O  Q=half 
the  throw,  or  eccentricity. 

4.  Draw  main  valve  and 
seat  as  in  figs.  460  and  461 ; 

5.  Determine  from  fig. 
459  displacement  of  main 
valve  for  crank  position  O  E, 
and  draw  valve  in  this 
position  as  in  fig.  462; 

In  fig.  459  draw  Q  M 
perpendicular  to  O  E  ex- 
tended which  gives  the  dis- 
placement. 

Fig.  462  shows  the  valve 
in  this  position.  This  is  the 
position  of  the  main  valve 
when  the  crank  is  at  V« 
stroke,  the  point  of  cut  off 
by  riding  valve. 

The  crank  and  eccentric 
position  corresponding  to 
that  of  the  main  valve  are 
shown  at  the  right. 

It  will  be  observed  that 
the  valve  is  practically  fully 
open  and  about  to  change 
its  direction  of  travel. 

If  the  angular  advance 
of  the  riding  eccentric  be 
made  Q',  fig.  459,  for  Vs  cut 
off,  such  that  the  riding  valve 
will  be  in  the  neutral  position, 
that  is  0',  will  be  on  O  E, 
the  riding  valve  will  be 
traveling  at  its  maximum 
velocity,  tending  to  give  a 
sharp  cut  off  which  is  to  be 
desired. 

In  fig.  459,  the  main 
valve  for  crank  position  O  E 
(Vs  cut  off  j  is  displaced  the 
distance  Q  M,  or  its  equal 
Q'  M'.  Now,  if  the  riding 
valve  had  zero  lap,  the  main 
valve  port  would  still  be 
covered  by  the  distance  Q' 
M'.  Hence,  if  cut  off  is  to 
occur  at  O  E  (  Vs  stroke), 
the  riding  valve  must  have 
a  negative  lap  equal  to  Q'  M', 


VARIABLE  CUT  OFF 


267 


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268 


VARIABLE  CUT  OFF 


6,  Determine  if  the  port  opening  for  Vs  cut  off  be  not  less  than  the  limit 

Fig.  462  shows  the  positions  of  the  two  valves  at  Vs  cut  off,  their  centers  being 
displaced  a  distance  Cr  Cm^  If  the  crank  be  rotated  backward,  the  port  will  be  opened 
by  a  movement  of  the  rnain  valve  to  the  left,  and  a  movement  of  the  cut  off  valve  to  the 
right.  Hence,  for  position  of  3^  port  opening  the  crank  must  be  rotated  backward 
until  Cr,  reaches  the  position  C'r,  with  respect  to  Cm,  such  that  C'r  Cm  =Cr  Cm  —  3^ 
in.  This  position  is  obtained  as  in  fig.  464,  the  valves  and  positions  of  eccentrics  being 
shown  in  fig.  463.  The  figure  shows  that  the  port  opening  C  D,  of  the  main  valve  is 
less  than  C  D',  of  the  riding  valve  by  an  amount  equal  to  D  D''.  At  no  point  of  admis- 
sion does  the  port  opening  become  ^"  because,  as  is  evident,  if  the  crank  be  turned 
backward  the  main  valve  closes;  if  forward,  it  opens,  but  the  riding  valve  closes,  hence, 
the  design  must  be  modified  to  obtain  not  less  than  ^"  port  opening  through  both 
valves. 


Scale: 
half  size 


Fig.  465. — Bilgram  diagram  for  modification  of  main  valve  and  riding  eccentric  setting  to 
give  3^  in.  effective  port  opening  for  V5  cut  off.  The  diagram  is  constructed  in  the  usual 
way  giving  Q,  for  the  modified  main  egcentric,  and  the  new  lap  circle.  Through  Q.draw  Q  T, 
parallel  with  Vs  cut  off  crank  position  O  E  Vs  C.  O.  If  the  original  negative  lap  of  the  riding 
valve  be  retained,  its  travel  will  remain  the  same  but  the  angular  advance  will  be  slightly 
changed.  With  radius  =  the  negative  lap  and  center  on  the  smaller  travel  semi-circle,  describe 
an  arc  tangent  to  Q  T,  giving  Q',  the  new  position  of  the  riding  eccentric.  For  position 
O  E 1/5  C.  O.,  the  main  valve  is  displaced  a  distance  Q  A,  hence  the  riding  valve  to  cut  off  at 
this  point  must  be  displaced  this  distance  minus  its  negative  lap  that  is  Q  A  —  0'  N,  or  Q'  A'. 


7.  Modify  design  for  Y^  in.  port  opening  at  Vk  cut  off; 

This  may  be  done  by  re-designing  the  main  valve  for  a  larger  port  opening,  say 
11/16,  as  in  figure  465. 


VARIABLE  CUT  OFF 


269 


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VARIABLE  CUT  OFF  271 


The  diagram,  fig.  470,  gives  the  displacement  of  the  valves  for  the  two  cut  oflFs, 
and  figs.  471  and  472,  the  crank  positions  for  }/^  port  opening  of  the  riding  valve  for  the 
]4  and  ^  cut  off  settings  of  the  riding  eccentric. 

Figs.  473  and  474  show  the  positions  of  the  valves  corresponding  to  the  14  and  }4 
cut  off  respectively. 

Fig.  473  indicates  that  the  later. cut  offs  are  "sluggish,"  the  valves  traveling  in 
the  same  direction  at  almost  the  same  speed.  From  the  positions  of  the  eccentrics 
shown  at  the  right,  evidently,  the  main  valve  is  traveling  the  faster,  hence  the  riding 
valve  will  reopen  the  port,  but  as  the  main  valve  cuts  off  at  this  point,  re-admission  will 
not  occur. 

Fig.  474  shows  a  sharper  cut  off  at  3^  stroke.  Here  both  valves  are  still  traveling 
in  the  same  direction,  the  main  valve  being  almost  stationary  while  the  riding  valve 
is  traveling  at  about  maximum  velocity. 


EK2C.O. 

E^/8  CjO. 


0 

Scale:  full  size 

Fig.  470. — Diagram  for  %  and  J^  cut  off  of  the  riding  valve.  Evidently  for  any  cut  off,  the 
displacement  of  the  riding  valve  is  equal  to  the  displacement  of  the  main  valve  less  the  negative 
lap  of  the  riding  valve.  Hence,  describe  an  arc  about  Q,  equal  to  the  negative  lap  Q  A',  and  draw 
a  tangent  parallel  to  the  given  cut  off  position  of  the  crank,  cutting  the  ridmg  travel  circle. 
Thus,  for  O  E  J^  C.  O.,  the  main  valve  is  displaced  a  distance  Q  A.  If  the  riding  valve  is 
to  cut  off  at  this  point  it  must  be  displaced  from  the  main  valve  an  amount  equal  to  its  neg- 
ative lap,  or  0  A',  that  is,  it  is  displaced  a  distance  A  A',  on  the  other  side  of  the  neutral  axis 
corresponding  to  O  Cr,  in  fig.  473.  The  tangent  through  A',  gives  Q' ,  the  corresponding  position 
of  the  eccentric.  Similarly  for  J^  cut  off,  Q  B,  is  the  displacement  of  the  main  valve,  and 
QB  — QB',  or  B  B',  displacement  of  riding  valve,  Q"  being  the  corresponding  center  of 
the  eccentric.    Here  B  B',  corresponds  to  O  Cr,  and  B  Q,  to  O  Cm,  in  fig.  474. 

Fig.  466  shows  a  still  sharper  cut  off  at  Vs  stroke,  the  valves  in  this  case  moving 
.  in  opposite  directions,  the  main  valve  being  almost  at  rest,  and  the  riding  valve,  at 

maximum  velocity. 

Figs.  475  and  476  show  position  of  valves  for  J^  in.  port  opening  of  the  riding  valve 
for  the  Vi  and  }4  cut  off  settings  of  the  riding  eccentric.  The  port  opening  of  the 
main  valve  in  each  case  being  greater  than  }4  in.  but  less  for  }^  than  for  y%  cut  off. 

9.  Test  for  over  travel  of  the  riding  valve ; 

Figs.  473,  474  and  469  show  that  the  earlier  the  cut  off,  the  greater  the  angle  be- 
tween the  two  eccentrics.  In  other  words  the  shorter  the  cut  off,  the  greater  the  travel 
of  the  riding  valve  with  respect  to  the  main  valve  regarding  the  latter  as  stationary. 


272 


VARIABLE  CUT  OFF 


Hence,  assuming  no  overtravel  of  the  riding  valve  with  respect  to  the  main  valve,  at 
latest  cut  off,  it  is  desirable  to  know  at  what  cut  off  overtravel  begins,  because  the 
constant  running  of  the  engine  with  undertravel  would  cause  the  riding  valve  to  wear 
a  "shoulder"  on  the  main  valve,  causing  leakage  and  perhaps  a  knock  at  short  cut  off. 
Unless  there  be  overtravel  for  cut  offs  near  the  working  cut  off  (Vs  in  this  case),  the 
design  should  be  further  modified  and  the  range  of  overtravel  made  as  great  as  possible. 


E.it"P.O 


e:%  CO. 


Scale:  full  size 


EVec.o. 


Scale, 


Figs.  471   and  472. — Diagrams  for  obtaining  crank  positions  corresponding  to  }4  in.  port 
opening  of  the  riding  valve  for  J4  and  ^  cut  off  settings  of  the  riding  eccentric  respectively. 


Regarding  the  main  valve  as  stationary,  the  travel  of  the  riding  valve  on  the  main 
valve  may  be  regarded  as  obtained  from  an  imaginary  eccentric  of  such  throw  and 
angular  advance  as  to  duplicate  the  movement  of  the  riding  valve  with  respect  to  the  main 
valve  as  obtained  from  the  two  eccentrics;  such  imaginary  eccentric  or  radius  is  called 
the  virtual  eccentric,  from  which  the  cut  off  setting  at  which  overtravel  begins  is 


VARIABLE  CUT  OFF 


273 


274 


VARIABLE  CUT  OFF 


VARIABLE  CUT  OFF 


275 


easily  obtained.  For  this  setting,  clearly,  the  K  travel  of  the  riding  valve  on  the  main 
valve  is  equal  to  negative  lap  of  the  riding  valve  -{-width  of  the  end  bridge  of  the  main  valve 
as  in  fig.  477,  the  two  valves  being  shown  in  the  position  at  which  over  travel  begins, 
that  is  "line  and  line"  or  "zero"  over  travel  position-in  fig.  478.  Hence  for  this  setting, 
the  two  eccentric  centers,  Q  and  Q',  in  the  Bilgram  diagram  will  be  displaced  a  distance 
equal  to  Cf  Cm,  or  A-f  B  in  figs.  477  and  478.  Q  Q',  in  fig.  479  then  is  the  radius  or 
throw  of  the  virtual  eccentric. 

The  cut  off  corresponding  to  zero  over  travel  is  determined  as  explained  under  the 
figure,  being,  as  indicated  in  the  diagram,  fig.  479,  3^  stroke.  This  leaves  no  margin 
for  cut  off  later  than  the  working  cut  off,  and  in  practice  the  design  should  be  further 
modified  to  increase  the  range  of  over  travel.  A  remedy  would  be  to  increase  the  throw 
of  the  riding  eccentric. 

10.    Locate  the  seat  limit; 

This  is  done  by  the  same  method  as  explained  on  page  286,  fig.  504,  illustrating 
the  seat  limit  for  the  Meyer  main  valve. 


WIDTH    OF  END  BRIDGE 
JEGATIVE   LAP 


LINE  AMD  LINE  r^ 
OR  ^ 


Cm 


Figs.  477  and  478. — Detail  of  one  end  of  valves  showing  that  the  half  travel  of  the  riding  valve 
on  the  back  of  the  main  valve  or  virtual  half  travel  for  zero  over  travel  is  equal  to  riding 
negative  lap -\^ end  bridge  width.  Fig  477,  shows  both  valves  in  neutral  position,  and  478, 
valves  in  position  of  zero  over  travel. 

Evidently  that  portion  of  the  valve  which  over  travels  L,  is  in  balance  with  respect 
,      to  the  steam,  hence  the  shorter  the  length  of  the  seat  the  less  the  load  on  the  valve  due 
to  the  steam  pressing  it  down  on  the  seat. 

Features  of  Riding  Cut  Off  with  Variable  Angular  Ad- 
vance.— ^A  study  of  the  example  just  given  will  show  certain 
characteristics  of  the  gear  which  are  in  brief: 


2.  Increasing  the  angular  advance  of  the  riding  eccentric  shortens  the  cut  ojf. 

2,  The  cut  off  is  ** sluggish''  for  late  cut  off,  increasing  in  sharpness  with 
the  degree  of  expansion. 

3,  The  effective  port  opening  decreases  as  the  cut  off  is  shortened, 

4,  The  virtual  travel  increases  as  the  cut  off  decreases. 


276 


VARIABLE  CUT  OFF 


CO.  FOR  ZERO 
OVERTRAVEL 


Scale:  half  size 


■x-\ 


^^XijA- 


<\  ^^ 


\  \'^-V'\  \ 


^   ^ 


STROKE 


VIRTUAL  ECCENTRICITY 
FOR  ZERO  OVERTRAVEL 


VIRTUAL  HALF  TRAVEL  =^(QQ'   OR    ErE^,) 

Cr     \  Cm 


END  BRIDGE 


Figs.  479  and  480. — ^Application  of  Bilgram  diagram  for  determining  cut  off  setting  of  riding  valve 
for  zero  overtravel.  The  two  travel  circles  of  the  main  and  riding  eccentrics,  and  Q,  are 
transferred  from  465,  being  here  drawn  on  same  scale  as  the  valves.  With  Q,  as  center 
and  radius  equal  to  A  +B,  in  fig.  477,  describe  an  arc  cutting  the  riding  eccentric  travel  circle 
at  Q'.  Q  Q',  then  is  the  virtual  eccentric  for  zero  overtravel.  Draw  crank  position  O  E,  per- 
pendicular to  Q  Q'.  Evidently  Q  and  Q',  are  at  their  maximum  displacement,  that  is,  Q', 
is  at  half  travel  with  respect  to  Q,  hence  O  E,  is  crank  position  when  the  valve  ends  are  line 
and  line  or  at  zero  overtravel,  as  shown  in  fig.  480,  the  distance  Cr  Cm  =Q  Q\  being  called 
the  virtual  eccentricity.  From  fig.  480,  for  cut  off,  the  riding  valve  must  move  to  the 
right  a  distance  equal  to  the  width  of  the  end  bridge.  Hence  in  fig.  479,  on  Q  Q',  lay  off  Q'B  = 
width  of  end  bridge,  and  with  Q,  as  center  and  radius  Q  B,  describe  an  arc.  Draw  through 
Q',  a  tangent  to  this  arc  Q'  T,  and  O  E',  parallel  to  Q'  T.  O  E'  then  is  the  crank  position  for 
cut  off  corresponding  to  zero  overtravel.  Utilizing  the  main  eccentric  travel  circle  as  a  crank 
circle,  in  connection  with  the  dotted  line  construction  to  the  left,  the  piston  position  cor- 
responds to  O  E',  is  found  to  be  34  stroke,  the  design  giving  overtravel  for  cut  off  not  later 
than  about  }4  stroke. 


VARIABLE  CUT  OFF 


277 


VIRTUAL 
ECCtNTRiC 


VIRTUAL 

ANGULAR 

ADVANCE. 


Figs.  481  to  483. — ^The  virtual  eccentric.  By  definition:  the  virtual  eccentric  is  an  imag-> 
inary  eccentric  of  such  throw  and  angular  advance  that  if  keyed  to  the  main  shaft  and  con- 
nected with  the  riding  valve,  would  give  it  a  movement  over  the  main  valve  (regarded  as  at  rest) 

precisely  the  same  as  it  has  when  both  valves  are  moving.  Fig.  482  shows  both  valves  in  neutral 
position,  and  in  the  diagram  fig.  481,  O  E',  is  the  crank  position  of  cut  off  for  zero  overtravel. 
With  a  radius  equal  to  Q  Q'  (fig.  479  =  Cr  Cm,  fig.  4S0)  describe  a  circle  whose  center  is  o. 
The  diameter  of  this  circle  will  be  the  throw  of  t\\e  virtual  eccentric,  or  virtual  throw.  For 
cut  off  at  o  E\  evidently  the  riding  valve  must  move  to  the  left  a  distance  equal  to  the 
negative  lap.  Hence,  lay  off  o  B  =  negative  lap,  and  project  down  the  dotted  line  cutting 
the  virtual  throw  circle  at  Ey  Ev  then  is  the  center  of  the  virtual  eccentric,  and  its  eccen- 
tricity is  equal  to  o  Ev,  for  the  setting  giving  zero  overtravel. 


278 


VARIABLE  CUT  OFF 


Scale: 
half  size 


VQ  CO. 
SETTING 


Riding  Cut  Oflf;  Variable 
Lap. — This  method  of  riding 
cut  off  is  known  as  the  Meyer 
gear,  and  is  largely  used  in 
marine  engines.  The  riding 
valve  is  operated  by  a  fixed 
eccentric,  and  the  cut  off 
altered  by  varying  the  lap  of 
the  riding  valve. 

The  gear  consists  of  a  main 
and  riding  valve,  the  latter 
divided  into  two  plates  or  blocks 
connected  by  a  right  and  left 
handed  screw,  the  screw  serving 
as  a  valve  spindle  and  as  a 
means  of  varying  the  lap. 

The  riding  eccentric  is  fixed 
and  usually  has  a  throw 
greater  than  the  main  eccen- 
tric. Its  angular  advance  is 
90°  for  reversing  engines,  and 
a  little  less  than  90°  for 
engines  which  run  in  only 
one  direction.  In  this  gear, 
as  in  all  riding  gears,  cut  oflE 
takes  place  when  the  riding 


Figs.  484  to  487. — Detail  of  valve  ends  with 
riding  valve  at  end  of  virtual  travel, 
showing  undertravel  for  Ys  and  }^  cut 
offs,  and  overtravel  for  Vs  cut  oflf.  In  fig. 
484  imagine  Em  as  center  of  main  eccen- 
tric, fixed  in  such  position  that  the  main 
valve  is  in  the  neutral  position,  then 
Er,  E'r  and  E'V  are  centers  of  virtual  eccentric  for  the  riding  valve  for  throws  corresponding 
to  K,  3^  and  V5  cut  oflF  respectively.  As  shown,  the  virtual  eccentrics  are  at  one  end  ot 
the  throw  displacing  the  riding  valve  a  distance  equal  to  H  the  virtual  travel. 


VARIABLE  CUT  OFF 


279 


valve  is  at  a  distance  from  the  center  of  the  main  valve  equal  to 
its  lap,  that  is,  when  the  steam  edge  of  the  riding  valve  is  line 
and  line  with  the  steam  edge  of  the  bridge  of  the  main  valve. 
The  following  example  will  serve  to  illustrate  the  features 
of  the  Meyer  gear. 

Example. — Design  a  Meyer  valve  gear  for  an  8  X  10  marine  engine 
suitable  for  the  following  conditions  of  operation:    Speed  300  R.  P.  M.; 

E'/eC.O. 

CI' 

E*/6C.O 


-TRAVEL  OP  MAIN  VALVE.- 


-TRAVEL  OF  RIOINQ    VALVE- 


Scale:  full  size 

Fig.  488.— Bilgram  diagram  for  main  valve  of  Meyer  cut  off  gear,  showing  method  of  locating 
the  riding  eccentric  to  avoid  readmission  as  at  Q'.  If  Q',  be  located  above  Q  X,  a  line  drawn 
perpendicular  to  latest  cut  off  O  E  J^  C.  O.,  re-admission  will  not  occur. 

lead  j/fe;  cut  off  range  3^  to  Mi  by  riding  valve,  main  valve  cut  off  J^; 
connecting  rod  ratio  2:1. 

2.  Find  area  of  steam  port; 

For  a  steam  velocity  of  6,000  ft.  per  minute  through  steam  port. 

area  piston  X piston  speed  n^ 


area  piston  = 


6,000 

.7854  X  diameter2  =  .7854  X64  =50.27  sq.  ins. 


280 


VARIABLE  CUT  OFF 


substituting  in  (1) 


piston  speed  =2  X  —  X300  =500  ft. 


50.27X500      , 
area  = —  =4.19  sq.  ms. 


6,000 


2.  Find  width  of  steam  port; 

width  =  area  -^  length . 


(2) 


Scale:  half  size* 


Figs.  489  and  490. — Detail  of  trial  main  valve  and  seat  for  Meyer  cut  off.  On  A  B,  lay  off  the 
steam  port  C  E  =1^6  in.,  the  port  opening  C  D  =  width  of  port  +i^  =i?^6  in.,  and  the  bridge 
E  F  =?say  %  in.  Sketch  in  valve  end  in  extreme  position  as  in  fig.  490.  D,  will  be  the  steam 
edge.  Lay  off  D  H  =width  of  poTt=^\^p  in.,  and  draw  D  D'  and  H  H',  giving  the  steam 
passage  through  the  valve.  H  H' =  height  of  exhaust  cavity  +  thickness  of  metal  over 
cavity  =  width  of  port  C  E  +say  H  in.  =  1  X%  in.  The  steam  passage  through  valve  is  usually 
made  same  size  as  steam  port  so  as  to  reduce  friction.  I  I',  the  end  of  the  valve  is  located 
far  enough  beyond  H  H',  to  give  a  steam  tight  joint,  say  3^  in.  Locate  G,  the  exhaust 
edge  of  the  valve,  so  that  D  Q=outside  lap+port  (for  zero  inside  lap)  =i5^2+"/i6  =  1*'4' 
The  edge  G',  of  the  bridge  is  so  located  that  G  G'  =C  E.  The  center  line  O  O,  is  now  drawn 
half  way  between  F  and  G'.  The  center  line  Cm.  of  the  valve  is  now  located  at  a  distance 
to  the  right  of  O  O  =one-half  travel  cf  main  valve,  as  measured  from  the  diagram,  fig.  488. 
Fig.  489  shows  the  valve  and  seat  complete  with  valve  in  neutral  position.  The  method  of 
finding  the  seat  limit  is  later  explained. 


Call  length  .8  of  cylinder  diameter  =.8X8  =6.4,  say,  6.5  ins.,  then  substituting  in  (2) 

width  =4.19 -J- 6.5=  .64,  say  .69  or  %. 


VARIABLE  CUT  OFF 


281 


3,  Design  main  valve  \ 

The  crank  position  for  J/g  cut  off  and  Bilgram  diagram  are  constructed  in  the  usual 
way  from  the  given  data  as  in  fig.  488  and  the  main  valve  shown  in  detail  in  figs.  489  and 
490.  The  port  opening  is  made  a  little  larger  than 'the  port  {%  in.)  so  that  the  effective 
port  opening  at  short  cut  off  will  not  be  too  small. 

4»  Determine  travel  of  riding  eccentric; 

Since  the  engine  must  reverse,  the  angular  advance  of  the  riding  eccentric  is  made 
90°,  hence  its  center  Q',  in  fig.  488,  will  be  on  the  vertical  line  through  O.  To  guard 
against  re-admission  Q',  must  be  located  on  or  above  the  line  Q  X,  drawn  perpendicular 
to  O  E,  K  C.  O.,  the  latest  cut  off. 


E.^eco. 


E'7/BC-O- 


Scale:  full  size 

Fig,  491. — Diagram  showing  laps  for  various  cut  offs  of  Meyer  cut  off  gear. 


If  Q',  be  located  on  Q  X  (fig.  488) ,  and  the  riding  valve  be  given  a  negative  lap  equal 
to  0'  Q,  it  will  cut  off  and  immediately  re-admit  at  crank  position  O  E  (J^  C.  O.). 

If  the  center  of  the  riding  eccentric  be  located  at  Q",  below  Q  X,  the  riding  valve 
will  cut  off  and  immediately  admit  again  when  the  crank  is  at  O  E',  before  cut  off  by  the 
main  valve,  thus  disturbing  the  steam  distribution  to  the  cylinder;  hence,  the  im- 
portance of  correctly  locating  t|j^e  riding  eccentric,  in  this  case  giving  it  sufficient  throw, 
the  angular  advance  being  fixed. 


5.  Find  lap  for  earliest  }4>  ^"^  off,  and  for  latest  cut  off; 

Since  both  eccentrics  are  fixed  Q  and  Q',  in  fig.  491  remain  the  same  as  in  fig.  488. 
In  fig.  491,  draw  crank  positions  for  K  and  %  cut  offs,  and  through  O,  a  line  parallel  to 
O  E  K  C,  O. 

The  small  lap  circle  at  Q',  tangent  to  the  line  parallel  O  E  K  C.  O.,  gives  the  posiiive 
lap  for  %  cut  off.     ¥ot%  cut  off,  the  main  valve  is  displaced  a  distance    Q  A,    on 


282 


VARIABLE  CUT  OFF 


one  side  of  J4  C.  O.,  and  the  riding  valve,  a  distance  Q'  A'.  The  arc  described  about  Q\ 
and  tangent  to  a  line  Q  T,  through  Q,  parallel  to  O  E  J'^  C.  O.,  gives  the  negative  lap 
(Q'  A'O  for  Vs  cut  off. 

6,  Determine  width  of  riding  valve  blocks', 

The  blocks  evidently  must  be  wide  enough  so  they  will  not  re-admit  steam  by  the 
back  edges  when  at  the  end  of  the  virtual  travel. 

For  shortest  cut  off  the  blocks  are  farthest  apart,  hence  this  setting  and  the 
virtual  half  travel  must  be  considered  in  determining  the  width.  Thus  at  shortest 
cut  off,  width  of  blocks  =lap  -{-width  of  port  -{-virtual  half  travel  -{rseal. 

Thus,  fig.  492  shows  main  valve  and  one  block  in  neutral  position  with  positive 
lap  A  B,  for  shortest  cut  off.     From  steam  edge  of  block,  lay  off  to  the  right  the  positive 


WIDTH  OF  PORT 

VIRTUAL  HALF  TRAVEL 


TOTAL  LAP  ADJUSTMENT 
POSITIVE  LAP 


Fig.  492. — Method  of  finding  width  of  block  of  Meyer  cut  off  gear. 

Fig.  493. — Modified  main  valve  for  Meyer  cut  off  gear  showing  new  location  of  the  steam 
port  H"  D"  in  top  of  valve  to  permit  lap  adjustment  of  blocks  for  latest  cut  off. 


lap  A  B,  and  project  up  to  A'  B'.  From  B',  lay  off  the  width  of  port,  virtual  half  travel 
and  seal,  making  the  latter  say,  H  inch,  giving  C,  which  locates  the  inner  edge  of  the 
bloclc.    • 

7.  Modify  steam  passage  of  main  valve  to  permit  lap  adjustment  of  blocks ; 

In  fig.  493  first  draw  the  block  of  length  just  found.  From  the  inner  end  I,  of  block 
lay  off  positive  lap  for  H  cut  off  and  negative  lap  for  J/^  cut  off,  as  shown,  thus  locating 
the  center  line  O  O,  of  the  riding  valve  for  %  cut  off  setting. 

Draw  main  valve  referred  to  O  O,  and  locate  edges  H  D,  of  the  steam  passage 
through  the  main  valve.    The  steam  passage  instead  of  being  straight  and  terminating  • 
at  H'  D',  as  in  the  preliminary  design,  must  be  curved  outward  and  terminate  at  H"  D", 
to  permit  negative  lap  adjustment  for  late  cut  off.    The  point  H",  is  located  at  a  distance 
from  the  steam  edge  L,  of  the  block  equal  to  the  positive  lap  of  earliest  cut  off. 


VARIABLE  CUT  OFF 


283 


8.  Determine  characteristics  of  the  gear; 

Construct  diagram,  fig.  494,  showing  valve  displacements  for  ^,  i^  and  3^  cut 
offs,  and  diagram,  fig.  495,  showing  valve  displacements  at  middle  of  admission  periods 
for  ^,  ^  and  %  cut  off.  settings.  From  these  diagrams  one  half  section  of  valves  aa-e 
drawn  m  position  corresponding  to  the  cut  offs,  and  mid-admission  positions  respec- 
tively as  in  figs.  496  to  498. 

The  figures  show  that  the  sharpness  or  rapidity  of  cut  off  increases  as  the  cut 
off  is  shortened,  the  valves  moving  in  the  same  direction  for  ^  and  ^  cut  off,  and  ia 
opposite  directions  for  H  cut  off. 


E  %  CO 


E  '/zC.O. 


E.  ^4  CO. 


Scale:  half  size  P^ 

Fig.  494. — ^Valve  displacement  diagram  ior  %,  }4  and  K  cut  off. 


Cut  off 
fositions 


Mid-admission 
positions 


Scale:  half  size 


Fig.  495. — ^Valve  displacement  diagram  for  mid-admission  crank  positions  O  E,  O  F,  and  O  G 
corresponding  to  ^,  J^  and  %  cut  off  respectively. 


Figs.  499  to  501  indicate  that  for  mid-admission  positions,  the  effective  port  opening 
is  greater  for  the  ^  cut  off  setting  than  for  either  the  ^  or  3^  cut  off  settings. 

The  reason  the  port  is  not  fully  open  in  fig.  499  is  because  the  port  opening  of  the 
main  valve  exceeds  the  width  of  the  port.     Henoe  in  such  case  the  steam  passage 


284 


VARIABLE  CUT  OFF 


V^CUT  OFF  Cr      0 


Figs.  496  to  498. — Positions  of  valves,  eccentrics, 
and  crank,  for  %,  K  and  K  cut  ofE.  By  noting 
the  positions  of  the  eccentrics  it  is  evident  that  as 
the  cut  off  is  shortened  it  becomes  sharper.  Figs. 
496  and  497  show  valves  moving  in  same  direction, 
and  fig.  498,  valves  moving  in  opposite  directions. 


Scale:  half  size 


VARIABLE  CUT  OFF 


285 


*4  CO.  SETT 


Scale:  half  size 


Figs.  499  to  501. — Positions  of  valves,  eccentrics  and  crank  for  mid-admission  corresponding 
to  K,  H  and  H  cut  offs,  showing  effective  port  opening    at  these  positions. 


286 


VARIABLE  CUT  OFF 


through  the  valve  should  be  widened  at  A   (fig.  499)  to  A',  making  A  A'  =  difference 
between  the  port  opening  of  main  valve  and  width  of  port  in  valve. 

It  should  be  noted  that  the  effective  port  opening  in  fig.  501  is  not  the  maximum 
for  }4  cut  off,  as  by  observing  the  positions  of  the  eccentrics,  it  will  be  seen  that  the 

greatest  opening  occurs  just  after  the  rnid-admission  position.     The  small  port  opening 
ere  obtained  at  early  cut  off  will  indicate  the  necessity  of  designing  the  main  valve 
for  large  port  openings  where  the  engine  is  to  be  worked_at  early  cut  offs. 

Scale:  half  size 


'/fe  VIRTUAL  TRAVEL 

>L-^B 


NEG.LAP 


NE6.  LAP.  FOR  ZERO 
Q        OVERTRAVEL  £^ 


ZERO.OVERTRAVEL 


VIRTUAL  HALF  TRAVEL 


Figs.  502  and  503. — Detail  of  valve  end  and  diagram  for  finding  cut  off  setting  of  the  blocks 
corresponding  to  zero  overtravel. 

9,  Test  for  overtravel; 

Draw  one  end  of  main  valve  as  in  fig.  502.  Lay  off,  from  end  of  valve,  A  B  =H 
virtual  travel,  then  C  D,  is  the  negative  lap  setting  for, zero  overtravel.  In  the  diagram 
fig.  503,  describe  the  negative  lap  circle  with  radius  Q'A=CD,in  fig.  502.  Draw 
tangent  Q  T,  and  crank  position  O  Eq.  parallel  to  Q  T;  then  O  Eq,  is  cut  off  settm^  for 
zero  overtravel. 


SEAT    LIMIT 


HALF  TRAVEL 

Cm      j_       O 


Fig.  504. — Seat  limit  for  Meyer  main  valve. 


10,  Locate  seat  limit. 

Draw  end  of  valve  in  extreme  position  or  at  the  end  of  its  travel  as  in  fig.  504. 
From  the  exhaust  edge  G,  of  the  valve,  lay  off  the  seal,  G  S,  say  J4  inch,  giving  the 
point  S,  which  is  the  seat  limit. 


VARIABLE  CUT  OFF  287 


Features  of  Riding  Cut  Off  with  Variable  Lap. 

From  the  example  just  given  illustrating  the  design  of  Meyer 

gear  for  a  marine  engine,  it  will  be  noted  that: 

i.  Increasing  the  lap  of  the  riding  valve  (that  iSj  moving  the  blocks  apart) 
shortens  the  cut  off; 

2.  The  cut  off  is  ''sluggish"  for  early  and  late  cut  offy  hut  somewhat  improved 
for  intermediate  cut  offs; 

3.  The  effective  port  opening  decreases  as  the  cut  off  is  shortened; 

4.  Where  very  early  cut  off  is  desired,  the  main  valve  should  he  designed 
for  large  port  opening,  to  secure  adequate  effective  port  opening  at  early  cut  off; 

5.  For  reversing  engines,  the  angular  advance  of  the  riding  eccentric  should- 
he  90°  to  secure  symmetrical  distribution  for  both  forward  and  reverse  motions; 

6.  For  engines  running  in  only  one  direction  the  angular  advance  of  the 
riding  eccentric  is  usually  a  little  less  than  90°; 

7.  Re-admission  is  avoided  by  the  proper  location  of  the  center  Q',  of  the 
riding  eccentric; 

8.  The  length  of  main  valve  may  be  reduced  by  shortening  the  latest  cut  off 
of  riding  valve. 

Riding  Cut  Off;  Variable  Travel. — This  method  of  variable 
cut  off  is  shown  in  fig.  505  to  512.  For  illustration  and  com- 
parison the  main  valve  of  the  Meyer  gear  shown  in  fig.  489  is  used 
with  the  same  travel  and  angular  advance.  The  maximum  throw 
of  the  liding  eccentric  is  made  the  same  as  for  the  Meyer  gear. 
The  amount  of  lap  to  be  given  the  riding  valve  will  depend  on 
the  earliest  or  latest  cut  off  and  angular  advance  of  the  riding 
eccentric. 

Taking  Ql,  fig.  505,  for  latest  cut  off  with  angular  advance  a  little  less 
than  90°,  then  if  the  earliest  cut  off  is  to  be  say,  zero,  the  negative  lap 
necessary  is  equal  to  the  lap  plus  the  lead  of  the  main  valve,  because  a  line  * 
Q  A,  through  Q,  parallel  to  crank  position  (E.O.C.O.)  is  above  at  a  distance 
—lap-\-lead. 

The  radius  of  the  negative  lap  circle  thus  is  equal  to  lap -{-lead  of  main 
valve. 

For  latest  cut  off,  describe  a  negative  lap  circle  through  Ql,  and  draw- 
tangent  QT.  A  line  Qo  E.L.C.O.,  parallel  to  OT,  gives  crank  position 
for  latest  cut  off. 


288 


VARIABLE  CUT  OFF 


E.L.C.O. 


E'/6C.O. 


Scale:  half  size 


Figs.  505  to  508. — Bilgram  diagram  for  riding  cut  off  with  variable  travel  and  positions  of  valves, 
eccentrics  and  crank  for  latest,  one-sixth,  and  zero  cut  offs. 


VARIABLE  CUT  OFF 


289 


LATEST 
C.O.SETTING 


Scale:  half  size 


Figs.  509  to  512. — Bilgram  diagram  and  positions  of  valves,  eccentrics  and  crank  for  mid- 
admission  corresponding  to  latest,  one-sixth  and  one-fourth  cut  offs,  showing  effective  port 
opening.  The  diagrams  show  the  gradual  reduction  in  port  opening  as  the  cut  off  is  short- 
ened, a  defect  inherent  in  this  type  of  variable  cut  off  gear. 


290  VARIABLE  CUT  OFF 


For  3^  cut  off,  draw  QB,  parallel  to  OE  J^  C.  O.,  and  describe  a  second 
lap  circle  tangent  to  QB,  and  center  on  line  QoM,  giving  the  eccen- 
tricity Qo  Q'^^  for  H  cut  off. 

Figs.  505  to  508  show  position  of  valves,  eccentrics  and  crank  for  latest, 
3^,  and  zero  cut  offs.  By  observing  the  position  of  the  eccentrics,  the 
quality  or  sharpness  of  the  cut  off  may  be  judged. 

In  fig.  509  QoE,  QoF  and  QoG,  are  mid-admission  crank  positions  cor- 
responding to  cut  off  settings  of  latest,  3^  and  }^  cut  offs  respectively „ 

The  valve  positions  corresponding  to  OqE,  OqG,  and  OoF,  respectively 
are  shown  in  figs.  510  to  512,  from  which  it  will  be  noted  that  the  effective 
port  opening  at  mid-admission  position  rapidly  decreases  as  the  cut  off 
is  shortened. 

Features  of  Riding  Cut  Off  with  Variable  Travel. — 

A  study  of  figs  505  to  512  indicates  the  following  characteristics 
■of  this  gear: 

1,  Reducing  the  travel  of  the  riding  valve  shortens  the  cut  off; 

2,  If  the  range  of  cut  off  be  up  to  zero,  the  negative  lap  must  he  equal  to  lap 
plus  lead  of  the  main  valve; 

3,  For  given  angular  advance  and  travel  of  the  riding  valve,  latest  cut  off 
depends  on  the  lap  of  the  riding  valve; 

4,  The  effective  port  opening  decreases  rapidly  as  the  cut  off  is  shortened; 

5,  Sharpness  of  the  cut  off  decreases  as  the  cut  off  is  shortened. 


MODIFIED  ^LIDE  VALVES 


291 


chaptp:r  7 

MODIFIED   SLIDE  VALVES 


Balanced  Slide  Valves. — Since  the  common  D  slide  valve  is 
only  adapted  to  moderate  steam  pressures,  it  is  necessary  where 


Fig.  513. — The  Richardson  balanced  slide  valve.  Packing  strips  S.  S',  are  let  into  the  top  of  th<!i 
valve  so  as  to  bear  against  a  plate  P,  thus  excluding  steam  from  the  top.  A  hole  O,  allpws 
any  steam  which  might  leak  past  the  packing  to  escape  into  the  exhaust  cavity  V.  R  is  a 
shifting,  or  relief  valve  for  use  on  locomotives  to  admit  air  into  the  steam  chest,  and  prevent 
it  being  drawn  in  through  the  exhaust  pipes  when  steam  is  shut  off,  and  the  action  of  the 
piston  creates  a  partial  vacuum  in  the  steam  chest. 


high  pressures  are  used,  that  there  be  some  means  of  balancing 
to  prevent  excessive  friction  and  wear.  This  is  done  by  ex- 
cluding the  steam  from  the  top  of  the  valve  so  that  its  pressure 
cannot  be  exerted  in  a  direction  to  press  the  valve  against  its  seat. 

Fig.  513  shows  one  method  of  accompHshing  this.    The  top  of  the  valve 


292 


MODIFIED  SLIDE  VALVES 


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MODIFIED  SLIDE  VALVES 


293 


is  provided  with  packing  strips  which  bear  against  a  plate  P,  attached  to 
the  steam  chest  cover,  thus  making  a  steam  tight  joint.  The  packing  is 
fitted  in  steam  tight  grooves,  and  held  in  contact  with  the  plate  by  springs 
underneath.  By  this  means  steam  is  excluded  from  the  space  between  the 
packing.  A  hole  O,  allows  any  steam  which  may  leak  past  the  packing  to 
escape  into  the  exhaust  cavity  V. 

The  several  methods  used  in  balancing  valves  will  be  illustrated  in 
describing  the  different  types. 


Piston  Valves. — This  type  of  valve  consists  of  two  pistons 


Fig.  516. — Piston  valve 
with  central  passage  lead- 
ing to  lower  port.  This 
type  of  valve  is  used 
where  the  steam  pipe  is 
attached  to  upper  cover 
and  is  objectionable  in 
that  the  central  pipe  is 
exposed  externally  to  the 
exhaust  steam  which 
lowers  the  temperature  of 
the  live  steam;  also  the 
steam  pipe  must  be  dis- 
connected to  remove  the 
upper  valve  cover. 


which  cover  and  uncover  the  ports  in  precisely  the  same  manner 
as  the  laps  of  the  plain  slide  valve  as  shown  in  fig.  514. 

A  and  A^  are  the  pistons  which  are  connected  by  a  central 
tube  T.  The  valve  works  in  the  short  barrels  or  bushings  B,  and 
B',  which  form  the  seat. 


294 


MODIFIED  SLIDE  VALVES 


The  annular  openings  O  and  O',  around  the  ports  form  the 
steam  passages  leading  to  the  cylinder  C.  The  valve  is  made  to 
work  steam  tight  by  means  of  the  packing  rings  shown  in  black. 

The  barrels  are  perforated  with  numerous  openings  as  S, 
through  which  the  steam  passes.  The  bridges  thus  formed  permit 
the  valve  to  work  back  and  forth  across  the  port  without  catching 


Fig.  517. — Double  admission  piston  valve.  An  annular  supplementary  steam  passage  A,  which 
acts  in  the  same  way  as  the  Allen  supplementary  passage,  gives  the  second  admission.  The 
valve  IS  of  the  inside  admission  type.  , 

or  jamming  as  would  otherwise  be  likely  to  occur  especially  on 
account  of  the  tendency  of  the  packing  rings  to  spring  out  into 
the  ports. 

Fig.  517  shows  a  double  admissionf  piston  valve.     The  prin- 
ciple is  similar  to  that  of  the  Allen  valve. 

An  annular  supplementary  passage  is  provided  which  gives  a  second 
admission.  Steam  is  taken  from  the  inside  and  exhausted  at  the  ends  as 
indicated  by  the  arrows.  On  account  of  the  surface  cut  away  by  the  supple- 
mentary port,  double  admission  piston  valves  are  seldom  provided  with 
packing  rings. 


MODIFIED  SLIDE  VALVES 


295 


The  Armington  and  Sims  valve  is  of  the  double  inside"^  ad- 
mission piston  type;  instead  of  the  annular  passage  as  in  fig.  517- 

Steam  passes  through  a  central  passkge,  being  admitted  at  the  inside 
and  exhausted  at  the  ends. 

A  double  ported  f  piston  valve  as  used  on  the  Ide  engine  is 
shown  in  fig.  518. 

This  is  also  of  the  inside  admission  type.    As  shown  in  the  figure,  steam 
is  admitted  from  the  central  cavity  to  the  cylinder  through  the  ports  B 


Fig.  518. — The  Ide  double  ported  valve  giving  double  admission,  but  only  one  opening  for 
exhaust.  Admission  is  from  the  inside,  entenng  the  steam  passage  through  the  ports  B  and 
C ;  exhaust  passes  through  the  valve  to  the  ends  of  the  cylinder. 

and  C,  and  exhausted  at  the  end  through  the  valve,  the  course  of  the  steam 
being  indicated  by  the  arrows. 


The  piston  valve  is  especially  adapted  to  compound  engines 
having  the  pistons  working  in  unison  (as  on  four  cylinder  loco- 
motives) or  having  the  cranks  180°  apart.  In  either  case  one 
valve  is  sufficient  for  the  two  cylinders. 


*N0TE. — In  multi-cylinder  engines  using  high  pressure  steam  this  is  an  advantage 
since  with  inside  admission  for  the  high  pressure  cylinder  the  packing  around  the  valve  stem 
is  not  exposed  to  the  high  initial  pressure. 

tNOTE. — The  difference  between  a  double  admission  and  a  double  ported  valve  should 
be  clearly  understood.  A  double  admission  valve  gives  two  openings  to  steam  both  of  which 
lead  the  steam  to  a  single  steam  port  in  the  seat,  as  shown  in  fig.  517.  A  double  ported  valve 
gives  two  openings  to  steam  but  a  separate  port  is  provided  for  each,  as  B  and  C,  f:^-  '^  !^- 


296 


MODIFIED  SLIDE  VALVES 


.  D     E   F  G         F 


Pig.  519. — Detail  of  Chandler  and  Taylor  balanced  piston  valve;  A,  BB,  steam  inlet  ports 
to  rings;  CCC,  steam  space;  DD,  snap  rings;  E,  connecting  ring;  F,  F,  wall  rings;  G, 
wedge  ring. 


Fig.  520. — Vauclain  piston  valve  of  the  Baldwin  four  cylinder  compound  locomotive.  The 
pistons  move  in  unison,  steam  being  distributed  to  the  cylinders  with  .a  single  valve  as 
indicated  by  the  arrows. 


MODIFIED  SLIDE  VALVES 


297 


As  applied  to  locomotives,  with   pistons  working  in  unison, 
the  arrangement  of  ports,  etc.,  is  shown  in  fig.  520. 

Live  steam  is  admitted  to  the  high  pressure  cyHnder  at  the  ends,  and 
exhausted  through  an  adjacent  port  in  the  valve,  from  -^hich  it  passes 
through  the  valve  to  an  admission  port  at  the  opposite  end  for  the  low 
pressure  cylinder.  The  final  exhaust  passes  only  through  a  central  depres- 
sion and  passage;  the  course  of  the  steam  through  the  engine  is  shown  by 
the  arrows. 


Fig.  521  illustrates  a  valve  for  a  compound  engine  with  cranks 
at  180° 


LOW  PRESSURE  CYLINDER 


HIGH  PRESSURE  CYLINDER 

Pig.  521. — Piston  valve  for  compound  engine  distributing  the  steam  to  both  cylinders.  The 
cranks  being  at  180°,  one  valve  suffices  for  both  cylinders.  The  arrows  indicate  the  path  of 
the  steam. 


The  central  part  of  the  valve  or  seat  is  surrounded  by  steam  which  is 
admitted  through  an  annular  port  to  the  annular  valve  space,  which  con- 
nects with  the  high  pressure  cylinder  as  shown. 

The  valve  has  just  opened  for  steam  to  the  upper  end  of  the  high  pressure 
cylinder,  and  the  exhaust  from  the  lower  end  is  just  entering  the  low  pressure 
cylinder,  while  the  low  pressure  exhaust  is  escaping  from  the  upper  exhaust 
chamber. 

The  steam  distribution  is  regulated  by  five  ports:  The  central  port 
admits  and  cuts  off  steam  to  the  high  pressure  cylinder  while  the  exhaust 
from  this  cylinder  passes  through  its  steam  ports  to  the  steam  ports 
of  the  low  pressure  cylinder  located  at  the  ends  of  the  seat.  The  exhaust 
from  the  low  pressure  cylinder  is  controlled  by  the  outer  edges  of  the  valve; 
at  the  upper  end  the  exhaust  passes  through  the  valve  as  indicated  by 


298 


MODIFIED  SLIDE  VALVES 


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MODIFIED  SLIDE  VALVES 


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Fig.  523. — Sectional  view  of  the  Reeves  compound  engine  with  cranks  at  180°,  showing  system 
of  piston  valves.  The  high  pressure  valve  at  the  right  is  only  for  admission,  the  other  valve 
distributing  the  steam  as  exhausted-  from  the  high  pressure  cylmder  to  the  low  pressure 
cylinder.    The  arrows  show  the  course  of  the  steam  in  passing  through  the  engine. 


^^^^  $TEAM  CHCST 


mm^^m^.^x^v. 


Pig.  524. — ^Reeves  double  ported  adjustable  admission  piston  valves. 


300 


MODIFIED  SLIDE  VALVES 


Steam  is  admitted  to  the  high  pressure  cylinder  by  a  piston  valve  having 
internal  admission  and  which  acts  as  an  admission  valve  only,  being  under 
control  of  the  governor.  The  exhaust  from  this  cylinder,  and  the  compres- 
sion of  both  cylinders  are  controlled  by  the  main  or  central  valve  which  is 
operated  by  an  eccentric  with  a  fixed  travel. 

It  is  obvious  that  any  change  in  travel  or  cut  off  of  the  admission  valve 
will  not  effect  the  cut  off  in  the  low  pressure  cylinder,  therefore,  changes  in 
load  and  consequent  cut  off  does  not  cause  excessive  compression  as  in  the 
usual  type  of  compound  engines. 


Fig.  525. — Balancing  cylinder  (B ) ,  for  balancing  the  weight  of  large  heavy  valves. 


On  large  vertical  engines,  provision  is  sometimes  made  to 
balance  the  weight  of  the  valve  and  thus  relieve  the  valve  gear 
from  considerable  friction  and  wear  as  shown  in  fig.  525. 

An  extension  S  of  the  valve  stem  is  connected  to  a  small  piston  A  which 
works  steam  tight  in  a  cylinder  B.  The  upper  end  of  the  balancing  cylinder 
does  not  admit  steam,  so  that  the  steam  pressure  acts  upward  on  the 
lower  face  of  the  small  piston  and  balances  the  weight  of  the  valve. 

The  Double  Ported  Valve.— The  difficulty  of  obtaining  suffi- 
cient port  opening  for  high  speed  engines  having  cylinders  of 


MODIFIED  SLIDE  VALVES 


301 


large  diameter  and  short  stroke  is  overcome  by  providing  double 
steam  ports  and  constructing  the  valve  to  open  them  in  unison 
as  shown  in  fig.  526.  It  is  equivalent  to  two  plain  slide  valves — 
a  long  valve  V,  superposed  upon  a  short  one  V,  each  having  equal 
steam  and  exhaust  laps. 


Fig.  526. — Double  ported  slide  valve.  There  are  two  openings  at  each  end  of  the  cylinder 
(A  B  and  A'  B')  for  admission  and  exhaust  of  steam.  The  valve  is  equivalent  to  two  plain 
slide  valves:  a  long  valve  V,  superposed  upon  a  short  one,  and  having  communicating  ex- 
haust passages  E  and  E'. 


EXHAUST^  ^  '  ^^"'^EXHAUSTr, 

Pig.  527. — ^Valve  of  the  Russel  engine  (Giddings  type).  Steam  enters  in  the  center  and  ex- 
hausts through  the  two  adjacent  cavities.  The  action  of  each  end  of  the  valve  is  similar 
to  that  of  the  Allen  valve;  the  course  of  the  steam  is  indicated  by  the  arrows.  To  prevent 
the  live  steam  lifting  the  valve  from  its  seat,  needle  ports  fnot  shown)  are  used,  one  connecting 
the  live  steam  space  within  the  valve  to  the  body  of  the  valve  chest,  and  the  second  con- 
necting the  exhaust  with  the  chest. 

The  inner  valve  V,  is  similar  to  a  plain  slide  valve  except  that  there  is 
communication  between  its  exhaust  space  E,  and  the  exhaust  space  E',  of 


302 


MODIFIED  SLIDE  VALVES 


the  outer  valve.  The  two  valves  form  one  casting;  steam  is  supplied  to 
the  inner  valve  through  the  passages  S  and  S',  which  communicate  with  the 
steam  chest  at  the  sides  of  the  valve.  Each  steam  passage  to  the  cylmder 
has  two  ports  A,  B,  and  A',  B',  and  each  port  is  made  one-half  the  width 
necessary  for  a  single  port;  hence,  the  travel  is  only  half  that  required  for  a 
single  ported  valve  having  the  same  area  as  the  port  opening.  The  valve 
is  balanced  by  means  of  an  equilibrium  ring  R,  fitted  to  the  back  of  the  valve 
as  shown. 


Fig.  528.— Pressure  plate  valve  of  the  Leffel  engine.  The  object  of  the  plate  C,  is  to  relieve  the 
back  of  the  valve  A,  from  the  pressure  of  the  steam,  this  pressure  being  carried  by  the  two 
distance  pieces  H,  I,  which  register  with  the  thickness  of  the  valve.  The  plate  with  its  de- 
pressions E,  F,  G,  forms  a  second  seat,  thus  making  the  valve  double  ported.  The  dotted 
lines  indicate  how  the  valve  and  plate  are  assembled. 

Pressure  Plate  Valves. — Most  automatic  cut  off  engines  of 
the  high  speed  type  are  fitted  with  valves  having  two  faces,  and 
which  provide  two,  three,  and  in  some  cases  a  greater  mmiber  of 
port  openings. 


MODIFIED  SLIDE  VALVES 


303 


The  usual  construction  is  shown  in  fig.  528.  The  valve  A, 
consists  of  a  long  thin  rectangular  plate  which  works  between 
the  valve  seat  B,  and  the  pressure  plate  C.  This  forms,  in  fact, 
a  second  seat  having  depressions  E,  F,  G,  corresponding  to  the 
steam  and  exhaust  ports  E',  P',  G'.  By  means  of  the  rectangular 
openings  in  the  valve,  steam  admitted  to  the  ports  in  the  pres- 
sure plate  passes  to  the  ports  in  the  seat  B.  The  valve  is  there- 
fore double  ported. 

The  pressure  of  the  steam  on  the  back  of  the  plate  is  carried  by  two 
projecting  strips  or  distance  pieces  H,  and  I,  which  correspond  to  the  thick- 
ness of  the  valve,  thus  relieving  the  latter  from  the  pressure  of  the  steam. 


Fig.  529. — The  Sweet  pressure  plate  valve.  C,  is  the  pressure  plate  which  relieves  the  valve 
of  the  steam  pressure.  This  is  a  double  ported  valve  with  the  second  admission  entering 
through  the  passage  A,  A  separate  passage  B,  is  used  for  the  second  exhaust  as  seen  in  ex- 
haust position  at  the  other  end  of  the  cylinder. 

By  means  of  two  adjusting  screws  M,  and  N,  the  ports  in  the  pressure  plate 
are  brought  opposite  those  in  the  seat. 

The  action  of  pressure  plate  valves  is  best  seen  from  sectional  views 
showing  the  valve  in  its  lead  position  as  shown  in  the  accompany  cuts. 


Fig.  529  illustrates  the  Sweet  valve  which  embodies  all  the 
principal  features  of  valves  of  the  pressure  plate  type. 

It  is  a  double  face  valve,  steam  being  admitted  at  the  extreme  ends  of 
the  valve,  there  being  two  steam  edges  at  each  end  giving  double  port 
opening,  as  shown  by  the  arrows. 

The  passage  A,  conveys  steam  from  the  shallow  recess  in  the  pressure 
plate  to  the  main  port. 


304 


MODIFIED  SLIDE  VALVES 


Fig.  530. — Sweet  valve  and  valve  stem,  showing  valve  assembled  in  valve  chest  of  Ames  engine, 
and  parts  dissembled.  The  valve  with  stem,  straps  and  pressure  plate  as  used  on  the  Ames 
engine.  The  valve  consists  of  a  rectangular  casting  accurately  finished  to  exact  thickness; 
it  operates  between  the  seat  and  pressure  plate  which  is  maintained^  at  the  proper  distance 
from  the  seat  by  the  two  strips  of  iron.  The  pressure  plate  is  held  in  position  by  two  fiat 
springs,  so  arranged  that  in  case  the  engines  receives  a  charge  of  water  the  pressure  plate 
is  forced  from  its  seat,  allowing  the  water  to  pass  directly  to  the  exhaust  pipe. 


MODIFIED  SLIDE  VALVES 


305 


The  chief  object  of  the  exhaust  passage  B,  is  to  secure  a  quick  opening 
and  closing  of  the  exhaust,  so  as  to  avoid  wire  drawing.  After  the  exhaust 
is  cut  off,  part  of  it  is  compressed  and  retained  in  this  space  before  Hve 
steam  enters  the  port.  Directly  after  cut  off  this  steam  is  allowed  to  mingle 
with  the  expanding  steam  in  the  cylinder. 

The  projections  D,  D',  are  for  the  purpose  of  protecting  the  finished 
surfaces  of  the  pressure  plate  from  the  cutting  action  of  the  exhaust  steam. 

In  fig.  531  is  shown  the  Woodbury  valve  which  combines  the 
steam  features  of  the  Sweet,  and  Allen  valves,  giving  four  port 
openings  to  steam,  and  two  to  exhaust. 


Fig.  531. — The  Woodbury  pressure  plate  valve.  This  valve  gives  quadruple  admission,  and 
double  exhaust.  The  dotted  lines  show  a  supplementary  passage  connecting  E  and  F;  this 
passage  acts  in  the  same  manner  as  on  the  Allen  valve. 

The  openings  A  and.  B,  act  in  the  same  way  as  those  of  the 
Sweet  valve. 

A  supplementary  passage  is  provided  along  each  side  of  the 
valve,  and  connects  the  steam  passages  E  and  F. 

This  passage  is  shown  by  the  dotted  lines  and  is  similar  in  its  action  to 
the  supplementary  passage  of  the  Allen  valve.  The  quadruple  admission 
and  double  exhaust  are  indicated  by  the  arrows. 

A  ledge  G,  is  provided  as  is  done  in  the  Sweet  valve  to  protect  the  finished 
surface  of  the  pressure  plate  from  the  action  of  the  exhaust  steam. 


A  valve  which  takes  steam  at  the  inside  instead  of  at  the  ends 


306 


MODIFIED  SLIDE  VALVES 


is  shown  in  fig.  532,  which  illustrates  the  valve,  and  used  on  the 
Armstrong  engine. 

This  valve  gives  four  openings  to  admission  as  indicated  in  the  figure.  The 
steam  pressure  tends  to  lift  the  plate  P,  and  it  is  therefore  held  down  on 
its  seat  by  means  of  the  bridle  B  B. 


Fig.  532. — The  Armstrong  pressure  plate  valve. 


S^555^5^^5^ 


^^^^^^^ 


Fig.  533.— The  Rice  pressure  plate  valve.    Double  admission  and  e.xhaust,  the  admission  being 
from  the  mside. 

Another  valve  taking  steam  from  the  inside  is  the  Rice  valve, 
illustrated  in  fig.  533. 

As  shown,  the  valve  gives  two  openings  to  admission  and  two  to  exhaust. 
The  relief  plate  consists  of  a  piston  aa,  fitted  to  a  cy Under  hh,  which  is  bolted 


MODIFIED  SLIDE  VALVES 


307 


to  the  floor  of  the  steam  chest.    The  piston  aa,  bears  against  distance  pieces, 
and  is  held  in  position  by  the  pressure  of  the  steam. 


Fig.  534. — The  Ball  valve  consisting  of  two  telescopic  cylinders  A  and  B,  which  are  pressed 
against  the  seats  by  pressure  of  the  steam  within.  A  flexible  connection  is  made  with  the 
valve  stem  by  the  two  projecting  fingers  C  and  D. 


VALVE 


STEAM    PASSAGES 

Figs.  535  and  536. — View  of  the  Ball  cylinder  and  valve,  showing  ports  in  the  lower  seat,  and 
the  circular  exhaust  passages.  These  indirect  passages  give  a  rather  large  clearance;  aside 
from  this  the  valve  possesses  some  good  features. 


308  MODIFIED  SLIDE  VALVES 

A  modification  of  the  telescopic  piston  and  cylinder  of  the 
Rice  valve  is  embodied  in  the  design  of  the  Ball  valve  as  illus- 
trated in  fig.  534. 

This  valve  consists  of  two  overlapping  cylinders  A  and  B,  having  parallel 
valve  faces  at  the  outer  ends.  Steam  is  admitted  to  the  interior  of  the 
valves  which  presses  each  face  against  its  corresponding  seat  in  the  steam 
chest.  The  admission  is  therefore  inside,  and  exhaust  outside  from  which 
it  passes  to  the  exhaust  pipe  at  the  bottom  as  indicated  in  the  figure.  The 
only  unbalanced  area  is  that  portion  of  the  steam  ports  which  is  opposite . 
the  cylindrical  part  of  the  valve  during  the  exhaust  period,  the  valve  being 
so  proportioned  as  to  leave  sufficient  unbalanced  pressure  to  secure  a  close 
contact  between  the  working  faces. 

A  flexible  joint  is  secured  with  the  valve  stem  by  means  of  the  two  fingers 
C,  D,  which  engage  in  a  grove  in  an  end  piece  attached  to  the  stem. 

The  valve  seats,  ports,  and  steam  passages  are  more  clearly  shown  in 
fig.  535,  and  the  valve  in  fig.  536.  This  valve  adjusts  itself  to  wear  and  has 
favorable  conditions  for  a  permanent,  steam  tight  joint  between  the  two 
cylindrical  parts;  it  has  the  disadvantage,  however,  of  a  rather  large 
clearance  space  and  indirect  steam  passages. 


LOOSE  ECCENTRICS  309 


CHAPTER  8 
REVERSING     VALVE     GEARS;     LOOSE     ECCENTRICS 


There  are  many  conditions  of  service  where  it  is  frequently 
necessary  to  reverse  the  motion  of  the  engine,  as  in  the  operation 
of  locomotives,  marine  engines,  traction  engines,  etc.  Numerous 
valve  gears  have  been  designed  by  which  this  is  quickly  and 
easily  done,  moreover  in  most  cases  a  considerable  range  of 
expansion  is  had  by  working  in  the  intermediate  positions. 

The  simplest  method  of  reversing  an  engine  consists  in 
rotating  the  eccentric  around  the  shaft  until  it  has  the  proper  angular 
advance  for  reverse  motion.  This  operation  is  shown  in  figs.  537 
and  538.  In  both  figures  the  crank  is  shown  in  its  mid  position. 
The  corresponding  positions  of  the  piston  and  valve  are  shown 
directly  above. 

In  fig.  537,  the  eccentric  is  set  to  run  the  engine  ahead.  To  reverse  the 
engine  the  valve  must  be  moved  an  equal  distance  to  the  left  of  its  neutral 
position  so  as  to  admit  steam  through  the  right  instead  of  the  left  port. 
This  is  done  as  shown  in  fig.  538,  the  eccentric  being  rotated  through  the 
arc  E  E',  making  the  angular  advance  A'  OE',  the  same  as  A  O  E.  This 
gives  the  valve  the  same  linear  advance  to  the  left  and  opens  the  right  port 
which  reverses  the  motion  of  the  engine.* 

A  simple  application  of  this  principle  is  shown  in  figs.  539  and  540. 

The  eccentric  E,  is  loose  on  the  shaft  between  a  fixed  collar  G,  and  a 
•    hand  wheel  H.    A  stud  projecting  from  the  eccentric,  and  passing  through 
a  curved  slot  in  the  wheel,  can  be  clamped  b}^  a  hand  nut  F. 


*NOTE. — It  should  be  noted  that  in  the  absence  of  indirect  rockers,  the  eccentric  is 
always  placed  hi  advance  of  the  crank,  that  is,  ahead  with  respect  to  the  direction  of  motion; 
hence,  the  direction  in  which  an  engine  will  run  is  easily  determined  by  noting  the  eccentric 
position. 


310 


LOOSE  ECCENTRICS 


When  running  forward  with  the  crank  at  C,  the  eccentric  center  is  at  E, 
and  the  nut  clamped  at  F. 

To  reverse,  steam  is  shut  off,  and  when  the  engine  stops,  the  nut  F,  is 
loosened,  then  moved  to  B,  and  clamped.  The  length  and  position  of  the 
slot  is  such  that  the  angular  advance  A  O  E  =  A'  OE',  when  the  hand  nut 


Figs.  537  and  538. — Simple  method  of  reversing  an  engine.  By  rotating  the  eccentric  on  the 
shaft  so  that  it  will  have  a  reverse  angular  advance  A'  O  E'  (fig.  538),  equal  to  the  forward 
angular  advance  A  O  E  (fig.  537),  the  valve  will  be  moved  from  M  to  M',  and  the  engine 
will  run  in  the  reverse  direction.    The  arrows  show  the  steam  distribution. 


F,  is  at  either  extremity  of  the  slot.     The  letters  are  the  same  as  in  figs. 
537  and  538  for  comparison. 


The  usual  method  of  rotating  the  eccentric  to  reverse  on 
marine  engines  is  shown  in  figs.  541  and  542. 


LOOSE  ECCENTRICS 


311 


Figs.  541  and  542  show  the  -construction  where  the  reverse 
gear  is  attached  to  the  main  shaft.  In  the  figures  the  eccentric 
E,  is  keyed  to  a  sleeve  V,  which  fits  so  as  to  easily  revolve  on  the 
main  shaft  S ;  any  movement  in  the  direction  of  the  shaft  is  pre- 
vented by  the  bearing  B,  and  collar  C. 

COLLAR 

ECCENTRIC  V— 1 


HAND  WHEEL 


Figs.  539  and  540. — Loose  reversing  eccentric;  an  application  of  the  principle  illustrated  in 
figs.  537  and  538.  The  eccentric  E,  is  free  to  turn  on  the  shaft  and  is  held  in  position  by  a 
stud  and  hand  nut  F.  The  stud  passes  through  a  circular  slot  in  the  wheel,  so  located  that 
when  the  stud  is  clamped  at  one  or  the  other  end,  the  eccentric  is  in  correct  position  for 
forward  or  reverse  motion  of  the  engine. 


A  spiral  slot  M,  is  cut  in  the  sleeve  and  hole  bored  in  the 
end  of  the  shaft  to  H.  A  straight  slot  is  cut  through  a  portion 
of  the  bore  from  H,  to  the  other  end  of  the  spiral  slot.  The  rod 
R,  works  in  the  bore  and  has  attached  to  its  end  cross  pins  P,  P', 
which  pass  through  the  shaft  and  sleeve  slots. 


312 


LOOSE  ECCENTRICS 


To  change  the  position  of 
the  eccentric,  R,  is  moved, 
which  by  the  action  of 
the  pins  in  traveling  the 
length  of  the  slots  causes 
the  sleeve  and  eccentric  to 
rotate  on  the  shaft,  thus 
changing  the  angular  ad- 
vance. 

By  giving  the  spiral  slot 
the  proper  pitch,  the  eccen- 
tric may  be  rotated  through 
the  correct  arc  when  P,  is 
moved  the  length  of  the 
slot  to  reverse  the  motion 
of  the  engine.* 

This  gear  as  applied  to 
engines  having  valves  on 
the  side  is  shown  in  plan 
in  fig.  543  which  illustrates 
the  construction  for  a 
compound  engine,  the 
cylinder  outlines  being 
shown  in  dotted  lines. 

The  eccentrics  Eand  E',  are 
keyed  to  a  valve  shaft  S',  which 
is  placed  directly  under  the 
valves  and  at  the  sides  of  the 
main  shaft  S. 


♦NOTE. — This  type  of  valve  gear 
cannot  be  used  to  vary  the  expansion, 
because  the  travel  remains  constant,  hence 
the  lead  becomes  excessive  for  intermediate 
positions  of  the  gear. 


LOOSE  ECCENTRICS 


313 


314 


LOOSE  ECCENTRICS 


Fig.  544. — End  view  of  fig.  543  showing  the  two  gear  wheels  G,  G',  which  transmit  motion 
from  the  main  shafts  to  the  spiral  slotted  sleeve  V,  and  eccentric  shaft  S'.  R,  is  the  reverse 
rod. 


Fig.  545. — End  view  of  loose  eccentric  reverse  gear  with  idler  between  main  shaft  and  valve 
shaft.  By  using  an  idler,  the  diameters  of  G,  and  G',  may  be  made  quite  small,  thus  reducing 
the  tangential  velocity  of  the  gear  wheels  which  is  desirable.  V,  is  the  spiral  slotted  sleeve; 
S,  eccentric  shaft,  and  R,  reverse  rod.  The  gear  G',  is  keyed  to  the  sleeve  at  K.  In  design, 
the  sleeve  should  be  thick  enough  so  that  it  can  be  firmly  keyed. 


LOOSE  ECCENTRICS 


315 


o-^  owe 


Motion  is  trans- 
mitted from  the  main 
shaft  to  the  small  or 
valve  shaft  S',  by  the 
gear  wheels  G,  G'; 
these  wheels  being  of 
the  same  size,  the 
two  shafts  revolve  at 
the  same  rate,  but  in 
opposite  directions,* 
the  valve  movement 
then,  is  indirect,  and 
the  eccentrics  are 
therefore  set  180** 
from  the  usual  posi- 
tions. 

The  gear  wheel  G  •, 
is  keyed  to  the  sleeve 
V,  which  fits  over 
the  valve  shaft,  and 
which  has  a  spiral  slot 
M,  and  a  turned  pro- 
jection C,  at  its  end. 

This  projection  or 
collar  and  the  gear 
wheel  prevent  any 
lengthwise  movement 
of  the  sleeve  as  it  re- 
volves in  the  bear- 
ing B. 

The  valve  shaft  is 
bored  to  the  point  H, 
and  has  a  straight  slot 
extending  from  H,  to 
P. 


♦NOTE.— An  end  view 
of  the  gears  G,  G',  is  shown 
in  fig.  544.  Sometimes  a 
third  gear  or  idler  is  used 
as  in  fig.  545.  Here  the 
motion  of  the  two  shafts 
are  in  the  same  direction, 
and  while  there  is  an  extra 
gear,  it  has  the  advantage 
of  reducing  the  speed  at 
the  circumference  which 
is  favorable  to  quiet  run- 
ning. 


316 


LOOSE  ECCENTRICS 


A  rod  R  is  inserted  in  the  bore  and  the  cross 
pin  P,  attached  in  the  same  rhanner  as  in  figs.  541 
and  542. 

Reversing  is  accomplished  by  sliding  R,  through 
the  bore,  which  by  the  action  of  the  slots  and  pins 
P,  P',  cause  the  valve  shaft  to  rotate  with  respect 
to  sleeve  V,  and  thus  change  the  eccentric  to  the 
position  for  opposite  motion. 


<u^  ^«       g  S  g 

O;       >    r<   G   ^   <o   rt 

t:a-5ggo|^ 

S  ^  <u  2^  ^  d  5 

60  o'w'o    .t^  St 
S  o*^  M^  ^S  M 

S;  O  <u      ni^  O 

■g-2  g"?  ^"^  d- 
<u  O  o  wiz.ti.o  g* 

V-  (u^:;  <u  ;>  0)  o  ^ 
O  o  S  rtw  o  ^  Q 


LINK  MOTIONS 


317 


CHAPTER  9 
REVERSING  VALVE   GEARS,   LINK  MOTIONS 


The  so-called  Stephenson*  Link  Motion. — This,  though 
one  of  the  earHest  forms  of  reverse  gear  is  probably  used  more 
extensively  than  any  other;  in  the  opinion  of  the  author  it  is  as 


Fig.  550.— r/ie  Williama  Link.  The  *f  olio  wing  quotation  from  Burgh's  Link  Motion  and 
Expansion  Gears  is  a  full  history  of  the  so  called  Stephenson  link  motion  including  conver- 
sation of  inventor  with  the  author  (Burgh).  Howe's  invention  was  suggested  by  the  Wil- 
liams link  shown  above.  "The  inventor  of  the  link  motion  in  its  simplest  original  and  best 
form  is  Mr.  W.  Howe,  who  introduced  it  in  the  month  of  August  in  the  year  1842.  He  was 
then  a  working  mechanic  in  the  employment  of  Messrs.  Robt.  Stephenson  &  Co.,  Engineers, 
Newcastle-on-Tyne.  The  history  of  the  invention  may  now  be  given  in  Mr.  Howe's  own 
language,  as  expressed  to  the  writer.  A  species  of  link  motion  (shown  above)  was,  just 
before  this  date,  suggested  by  Mr.  Williams  who  was  a  young  gentleman  apprentice  in  the 
works  at  the  time.  In  the  figures.  A,  indicates  the  crank  shaft  B,  the  proposed  link  C.  is 
the  connecting  rod,  connecting  the  link  to  the  valve  rod  D;  E,  are  two  eccentrics,  and 
F,  the  block  for  reversing  the  motion  of  the  valve  and  engine.  It  will  be  easily  seen  that 
the  suggestion  could  never  have  been  of  the  least  practical  use,  because  one  eccentric  bank 
would  displace  the  other  when  in  motion.  Several  persons  employed  in  the  works  saw  the 
drawing  Mr.  Williams  had  made,  and  amongst  them  Mr.  Howe,  but  no  one  brought  it  into 
a  state  for  practical  application  until  August  1842,  when  Mr.  Howe  made  a  pencil  sketch 
and  a  rough  wooden  model  of  his  link  motion,  and  both  of  the  originals  are  now  in  the 
South  Kensington  Museum.  This  model  so  perfectly  indicated  what  the  curved  link 
should  be,  that,  acting  uj^on  the  advice  of  his  friend,  Mr.  Howe  showed  it  to  Mr.  Hutchin- 
son, then  the  manager  of  Stephenson's  Works,  who  at  once  saw  the  worth  of  its  application 
practically,  not  one  as  a  reversing  but  also  as  an  expansion  gear  for  working  the  slide  valve, 
and  he  (Hutchinson)  sent  the  model  at  once  to  Mr.  Robert  Stephenson,  then  in  London, 
who  also  approved  of  it  immediately  he  saw  it.  At  the  time,  Mr.  Howe  was  engaged  in 
making  a  working  model  of  a  wedge  motion  for  two  locomotives,  being  built,  but  was  directed 
to  substitute  for  this,  his  link  motion.  He  then  made  a  full  size  model  and  proved  the 
adaptation  of  the  link  motion  for  any  grade  of  cut  off.  The  dimensions  were:  outside  lap 
one-half;  under  lap  one-sixteenth;  port  opening  1  in.;  throw  3:  length  of  eccentric  rods 
five  in. 


318 


LINK  MOTIONS 


REVERSE     LEVrf\ 
FORWARD 

QUADRANT 


STEM 


beautiful  a  piece  of 
mechanism  as  ever 
was  invented.  The 
name  shifting  link 
is  sometimes  used 
to  distinguish .  it 
from  the  stationary 
or  Gooch  link. 


The  Stephenson 
link  was  originally 
intended  for  revers- 
ing only,  but  within 
certain  limits  it  is 
used  to  advantage 
as  a  variable  cut  off 
or  so  called  expan- 
sion gear.  This 
feature  is  made  use 
of  especially  on  loco- 
motives, and  marine 
engines. 


As  shown  in  fig. 
551,  it  consists  of  a 
link   L,    block  M, 


Fig.  551.— The  so  called 
Stephenson,  or  shifting 
link.  There  are  two  ec- 
centrics E  and  E',  whose 
rods  R,  and  R',  are  con- 
nected to  the  Hnk  at  A, 
and  B .  When  A,  is  oppo- 
site the  block  M,  as 
shown,  the  engine  runs  in 
a  forward  direction.  To 
reverse,  lever  G,  is 
moved  to  G",  which 
brings  B,  opposite  the 
block,  thus  the  motion  of 
the  reverse  eccentric  is  im- 
parted to  the  valve  stem, 
and  the  engine  reversed. 


LINK  MOTIONS 


319 


-/. 


S' 


rm 


9 


T 


Fig.  552. — Plan  of  shifting  link  showing  double  reach  rods  S  and  S'.  With  two  rods  there  is  no 
lateral  or  twisting  strain  on  the  stem  in  reversing;  this  isa  point  well  worth  noting  by  anyone 
intending  to  purchase  an  engine,  the  ofTset  torm  of  construction  being  objectionable.^  The 
reach  rods  are  pivoted  to  the  link  at  C,C',  and  to  the  reverse  lever  G,  at  D,D'.  P  is  the 
valve  stem  pin. 

two  eccentrics  E,E',  and  eccentric  rods  R,  and 

R',  which  are  pivoted  to  the  link  at  A  and  B. 

The  valve   stem  has   a  forked   end,    and  is 

pivoted  to  the  block  by  the  pin  P.     Reach  rods 

S  and  S',  (one  on 
each  side  of  the  link) 
connect  the  latter 
with  a  notched  quad- 
rant H ,  and  latch  I  ^ 
which  retains  it  in 
any  position. 

The  link  which 
consists  of  two 
curved  bars  bolted 
together  at  the  ends, 
freely  slides  on  the 
block  when  the  re- 
verse lever  is  moved, 
and  to  a  limited  ex- 
tent in  operation. 

Fig.  553. — Upper  end  of  single  cylinder  marine  engine  showing  link  with  adjustable  block. 
The  link  is  provided  with  double  reach  rods  having  central  connection  on  each  side  of  the 
link  preventing  lateral  strain. 


320 


LINK  MOTIONS 


If  the  block  be  at  one  end  of  the  link,  the  motion  of  the  ec- 
centric attached  to  that  end  of  the  slot  is  transmitted  to  the  valve ; 
when  the  block  is  at  some  intermediate  position,  the  valve  re- 
ceives the  combined  motion  of  the  two  eccentrics ;  if  the  block  be 

at  the  middle  of  the  slot,  or  mid- gear, 
position,  the  valve  does  not  admit 
steam  to  the  cylinder.  As  shown 
in  the  figure,  the  bldck  is  at  that 
end  which  is  attached  to  the  for- 
ward eccentric  E,  hence  the  engine 
runs  in  a  forward  direction.  By 
moving  the  reverse  lever  to  G", 
the  link  slides  to  the  right  until  the 
other  end  P',  which  is  attached  to 
the  backward  eccentric  E',  is  in 
contact  with  the  block.  The  valve 
then  partakes  of  the  motion  of  this 
eccentric  and  the  motion  of  the 
engine  is  reversed. 

With  the  reverse  lever  in  any 
intermediate  position  between  full 
gear  and  mid-gear,  the  cut  off  is 
shortened, .  because  the  motion  of 
one  eccentric  tends  to  counteract 
that  of  the  other ;  the  combined  effect 
is  to  reduce  the  travel  of  the  valve. 

Fig.  554. — Small  marine  engine  fitted  with  an  offset  shifting  link;  an  objectionable  construe-  ■ 
tion._  When  the  link  is  not  central  with  the  axis  of  the  valve  stem  there  is  a  tendency  for 
the  link  to  turn  about  the  valve  stem  axis  every  J^me  the  link  is  shifted  by  the  reverse  lever 
and  also  during  operation  a  tendency  to  turn  to  and  fro  is  caused  by  the  slip  of  the  block. 
The  latter  effect  is  augmented  by  the  objectionable  location  ot  the  pivot  at  the  center  instead 
of  at  the  end  of  the  link  inasmuch  as  the  slip  is  increased  when  the  pivot  is  at  the  center. 
This  turning  tendency  is  resisted  by  providing  the  valve  stem  with  a  square  end  section 
working  m  a  bearing  as  shown.  Evidently  any  lost  motion  due  to  wear  will  allow  the  link 
to  get  out  of  alignment  and  sometimes  cause  it  to  work  roughly  or  stick  in  shifting.  The  only 
advantage  due  to  offsetting  the  link  is  that  it  allows  more  room  for  a  main  bearing.  In  the 
above  example,  the  square  section  of  the  valve  stem  should  be  much  larger  and  preferably 
shaped  as  a  flat  bar  of  a  width  considerably  greater  than  its  thickness.  The  bearing  should 
be  adjustable  for  wear. 


LINK  MOTIONS 


321 


Figs.  555  to  558. — Movement  of  the  link  during  one  revolution.  The  figures  show  the  positions 
of  the  link  gear  when  the  crank  C  is  on  the  dead  center,  and  at  H,  H  and  ^  of  a  revolution. 
The  point  of  suspension  being  at  the  center,  as  on  locomotives,  the  slip  is  considerable. 


322 


LINK  MOTIONS 


Some  of  the  different  positions  taken  by  a  link  for  one  revolution  of  the 
crank  are  shown  in  figs.  555  to  558,  which  illustrates  a  locomotive  link 
motion  in  full  gear  for  four  positions  of  the  crank.  Fig.  555  shows  the  gear 
with  crank  C  at  the  beginning  of  the  stroke;  the  other  figures  illustrate 
the  position  of  the  link  when  the  crank  has  made  34,  H,  and  %  of  a  revo- 
lution.* 

Ques.    What  is  the  difference  between  open  and  crossed 
rods? 

Ans.     The  eccentric  rods  are  said  to  be  open,  if  they  do  not 
cross  each  other,  when  the  eccentric  centers  lie  between  the  link 


Figs.  559  and  560. — Diagrams  illustrating  open,  and  crossed  rods.  In  shortening  the  cut  off 
by  "hooking  up,"  open  rods  give  increasing  lead,  crossed  rods,  decreasing  lead.  When 
it  is  intended  to  work  the  engine  linked  up,  as  with  a  locomotive,  it  is  advisable  to  have  the 
rods  open,  as  a  greater  range  of  expansion  is  obtainable  with  less  reduction  of  port  opening 
than  with  crossed  rods. 


and  shaft  center  as  shown  in  fig.  559.     If  the  reverse  condition 
obtain,  as  in  fig.  560,  the  rods  are  said  to  be  crossed. 

Ques.    What  is  the  effect  of  open  and  crossed  rods  on  the 
steam  distribution  ? 


*N0TE. — In  figs.  555  to  558  the  reach  rod  is  shown  attached  to  the  central  portion  of  the 
link  instead  of  at  the  end.  ^  This  construction  is  for  locomotives  on  account  of  the  position  of 
the  rocker  arm  but  the  action  of  the  link  is  not  so  good  as  when  the  attachment  is  at  the  end 
as  in  figs.  575  and  576. 


LINK  MOTIONS 


323 


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LINK  MOTIONS 


The  effect  of  open  and  crossed  rods  is  shown  in  figs.  562  to  565.  The 
first  two  figures  illustrate  why  the  lead  increases  with  open  rods  when  the 
link  is  moved  from  full  to  mid  gear.  On  account  of  the  inclination  of  the 
rods,  and  the  position  of  the  eccentric  centers  both  rods  tend  to  push  the 


Pigs.  562  and  563. — Diagrams  illustrating  why  open  rods  give  increasing  lead.  In  shifting 
the  link  trom  lull  to  mid  gear,  the  angularity  of  the  rods  is  so  changed  that  the  valve  stem 
pin  P,  and  valve  are  moved  to  the  left  a  distance  L,  thus  increasing  the  lead  this  amount. 

link  and  valve  to  the  left  at  the  beginning  of  the  movement.  The  upper 
rod,  after  passing  the  horizontal  position,  partially  counteracts  the  move- 
ment imparted  to  the  link  by  the  lower  eccentric  resulting  in  a  gradually 
increasing  lead  in  amount  equal  to  L.  The  position  of  the  link  center  for 
full  gear  (fig.  562)  should  be  noted. 

Figs.  564  and  565  show  why  crossed  rods  decrease  the  lead  from  full  to 


LINK  MOTIONS 


325 


mid  gear.  The  combined  effect  of  the  angularity  of  the  rods  is  such  that 
in  moving  the  hnk  from  fitll  to  mid  gear  the  Hnk  and  pin  P  are  moved  to  the 
right  a  distance  L,  this  decreasing  the  lead  by  that  amount.     • 

In  both  cases  the  valve  is  shown  in  one  of  the  positions  with  zero  lead, 
that  is,  in  line  and  line  position  to  clearly  illustrate  the  change  in  lead. 


Figs.  564  and  565. — Diagrams  illustrating  why  crossed  rods  give  decreasing  lead.  In  shifting 
the  link  from  full  to  mid  gear  the  angularity  of  the  rods  is  so  changed  that  the  valve  stem 
pin  P  and  valve  are  moved  to  the  right  a  distance  L,  decreasing  the  lead  this  amount. 

Short  rods  are  used  to  emphasize  the  effect  of  open  and  crossed  rods  on  the 
lead. 


Oues.     When  should  open  and  crossed  rods  be  used  ? 

Ans.     If  the  link  motion  is  intended  to  be  used  as  an  expansion 


y2Q 


LINK  MOTIONS 


gear,  on  a  locomotive,  open  rods  should  be  used  as  a  greater 
range  of  expansion  may  be  obtained  with  less  reduction  of  port 
opening  than  with  crossed  rods.*  If  the  link  is  to  be  used 
only  in  full  gear,  or  in  connection  with  an  independent  cut  off, 
crossed  rods  may  be  used,  and  the  link  made  straight. 

Oues.     How    early    may    steam    be    cut    off    with    the 
Stephenson  link? 


Fig.  566.— Reeves  link  motion  adjustable  cut  off  for  engine  driving  centrifugal  pumps,  fans, 
etc.  The  cut  off  may  be  varied  while  the  engine  is  in  motion.  The  parts  are:  A,  link;  B, 
link  block;  C,  D,  eccentric  rods;  E,  adjusting  block;  F,  adjusting  screw;  G,  adjusting  crank. 


Ans.  This  depends  on  the  amount  of  port  opening  at  full 
gear.  If,  as  with  locomotives,  the  port  opening  at  full  gear  be 
greater  than  the  width  of  the  port,  fairly  good  admission  may  be 
obtained,  cutting  off  as  early  as  one-quarter  stroke.  For  shorter 
cut  off,  the  admission  is  poor  and  one-sixth  stroke  may  be 
taken  as  the  minimum  cut  off  with  the  ordinary  valve. 


*NOTE. — On  locomotives  it  is  necessary  to  give  little  or  no  lead,  and  make  the  port 
opening  greater  than  the  port  for  full  gear  in  order  to  prevent  excessive  lead  and  too  little  port 
opening  at  early  cut  off. 


LINK  MOTIONS 


327 


Ques.     What  are  the  diflferent  forms  of  the  shifting  link  ? 

Ans.     The  slotted  link  as  already  described,  the  open,   the 
double  bar  marine  type,  and  the  box  link. 

The  open  link  is  similar  to  the  ordinary  link  but  differs  in  that  the  eccen- 
.tric  pins,  instead  of  being  attached  to  one  bar,  are  located  as  shown  in  fig. 
567.    With  this  construction,  the  eccentrics  must  have  a  larger  throw,  since 


M® 


Fig.  567. — The  open  link;  used  chiefly  on  British  locomotives  where  there  are  no  rockers. 
The  eccentric  rods  are  pivoted  at  A  and  B,  and  the  link  suspended  from  the  upper  rod  pin. 
The  fixed  point  of  the  reach  lods  is  below  the  central  line  of  motion. 


pm- 


jrn 


B 


•J 


"^W 


Figs.  568  and  569.— The  double  bar  link  as  used  on  marine  engines.  The  eccentric  rods  are 
pivoted  at  A,  B,  and  C,  D,  on  the  central  arc  of  the  link  which  improves  somewhat  the  steam 
distribution. 


328 


LINK  MOTIONS 


the  eccentric  pins  move  a  greater  distance  than  the  maximum  travel  of  the 
valve.  The  open  link  is  used  chiefly  on  British  locomotives  where  there  is 
no  rocker,  the  link  being  hung  from  the  upper  eccentric  rod  pin  with  reverse 
shaft  below  the  central  line  of  motion. 

The  double  bar  marine  type  link  is  shown  in  figs.  568  and  569.  It  con- 
sists of  two  bars  curved  to  the  proper  arc  and  connected  at  their  ends  by 
sleeve  bolts  which  retain  the  bars  at  the  desired  distance  apart.  The 
eccentric  rods  are  attached  to  two  pairs  of  pins  A,  B,  and  C,  D,  each  rod 
end  having  a  double  bearing.  A  third  pair  of  pins  E,  F,  receive  the  reach 
rods;  these  pins  may  be  either  located  at  the  center  as  shown,  or  at  the  end 


aLOGK  HAND  WHEEL 

Pig.  570  and  571. — Independent  cut' off  adjustment  for  link  motion;  usually  fitted  to  one  or 
more  cylinders  on  multi- cylinder  marine  engines.  This  permits  regulation  of  the  expansions, 
receiverpressures.etcso  as  to  get  a  steam  distribution  best  suited  to  the  running  conditions. 


as  in  fig.  575.  On  marine  engines,  an  independent  adjustment  for  cut'  off 
is  frequently  fitted  to  the  high  pressure  cylinder  valve  gear,  and  sometimes 
to  each  cylinder. 

With  link  motion,  the  independent  adjustment  as  shown  in  figs.  570and57l 
consists  of  an  arm  A,  keyed  to  the  reverse  shaft,  and  having  at  its  end,  a 
slot  within  which  works  a  block  with  screw  adjustment. 

The  reach  rods  are  attached  to  pins  which  project  from  the  block;  by 
turning  the  wheel.  W,  the  block  is  moved  in  the  slot  which  changes  the 
position  of  the  link  and  thus  alters  the  cut  off.  Fig.  572  shows  the  adjust- 
able cut  off  arm  as  fitted  on  marine  engines. 

The  box  form  of  link  which  has  the  pins  in  the  line  of  the  slot  itself  is 
shown  in  fig.  573.    Where  a  short  eccentric  throw  is  desired  the  box  link  is 


LINK  MOTIONS 


329 


used  to  advantage.     It  is,  however,  expensive  to  make  on  account  of  the 
difficult  construction. 

Oues      Why  is  a  link  slot  curved  ? 

Ans  To  equalize  the  lead  of  the  valve  for  all  travels.  The 
radius  of  the  link  is  so  proportioned  as  to  make  the  increase  or 
decrease  of  the  lead  the  same  for  both  strokes  of  the  piston.* 


ADJUSTABLE    ARW\ 

Fig.  572. — Independent  cut  off  adjustment  for  link  motion;  view  showing  gear  assembled  on 
engine.  The  reach  rods  are  pivoted  to  a  block  which  works  on  the. screw  S.  By  turning  this 
screw  at  W,  the  block  is  moved  in  the  f^lot  and  the  link  shifted,  thus  changing  the  cut  off. 

ECCE>rTR»C  ROD 
PIMS 


^^<'-cr: 


Figs.  573  and  574. — The  box  link.    Used  to  advantage  where  a  short  eccentric  throw  is  desired 
since  the  valve  travel  is  about  the  same  as  the  throw.    The  box  link  is  difficult  to  construct. 


Oues.     What  effect  has  the  action  of  the  link  on  release 
and  compression? 

*N0TE. — The  radius  of  the  link  is  a  little  less  than  the  length  of  the  eccentric  rod,  or 
about  twice  the  (lap+lead)  less  than  the  distance  from  the  center  of  the  link  block  to  the 
center  of  the  eccentric. 


330 


LINK  MOTIONS 


Ans.     As  the  cut  off  is  shortened  by  shifting  the  position  of 
the  Hnk,  these  events  occur  earlier. 

On  locomotives,  this  peculiarity  of  the  link  motion  is,  within  limits,  an 
advantage,  because  when  a  locomotive  is  running  fast,  steam  is  cut  off 
short,  and  early  release  and  compression  is  desirable  since  owing  to  the 


SLIP    WtTH    END    SUSPENSION 


SLIP   WITH    CCNTER     SUSPENSION 


CENTER     SUSPENSION 


Figs.  575  and  578. — Diagrams  illustrating  the  effect  of  end,  and  center  suspension.  When 
possible,  the  point  of  suspension  should  be  at  the  end  of  the  link  as  shown  in  fig.  575,  because 
the  slip  is  less  than  with  center  suspension  as  in  fig.  578. 


LINK  MOTIONS  33*^ 


high  piston  speed-,  more  time  is  needed  for  pre-release,  and  the  increased 
cushioning  due  to  the  early  compression  is  absorbed  in  bringing  the  re- 
ciprocating parts  to  rest.  The  clearance  space  is  thus  filled  with  steam  at 
a  higher  pressure,  which  reduces  the  amount  of  live  steam  required  to 
increase  the  pressure  in  the  clearance  space  to  that  of  admission. 

Oues.     What  is  the  ''slip?" 

Ans.  The  sliding  of  the  Hnk  on  the  block  which  occurs  during 
each  stroke. 

Oues.     Why  does  the  link  slip? 

Ans.  The  center  of  the  block,  being  pivoted  to  the  valve  stem, 
moves  in  a  straight  line,  while  the  ends  of  the  reach  rods  which 
guide  the  link  have  a  circular  movement,  hence  a  side  wise 
motion  is  given  to  the  link,  causing  it  to  slip  or  slide  on  the  block. 

In  addition  to  this,  slip  is  occasioned  by  what  might  be  called  "the 

•     angularity  of  the  link,"  that  is,  the  inclined  positions  which  it  takes,  cause 

a  sliding  action  as  indicated  in  figs.  575  to  578.    It  should  be  noted  that 

the  end  of  the  link  is  furtherest  from  the  block  when  the  link  is  in  the  nearly 

vertical  positions  shown  at  the  left  of  the  figures. 

Owes.     What  is  the  point  of  suspension? 

Ans.     That  point  where  the  reach  rods  are  pivoted  to  the  link. 

Oues.     What  is  the  fixed  point? 

Ans.  The  center  on  the  rocker  arm  at  which  the  reach  rods 
are  pivoted,  and  about  which  the  rods  swing;  the  swing  center 
of  the  reach  rods. 

Oues.  What  determines  the  position  of  the  point  of 
suspension? 

Ans.     The  type  of  engine,  and  conditions  of  operation. 

On  locomotives  the  link  is  usually  suspended  near  the  center,  but  where 
conditions  permit,  the  point  of  suspension  is  best  located  near  the  end. 

Figs.  575  to  578  show  the  two   locations  of  the   point   of  suspension. 
In  each  figure  the  link  is  shown  in  two  corresponding  positions  from  which 


332 


LINK  MOTIONS 


is  seen  the  effect  which  changing  the  point  of  suspension  has  on  the  sHp. 
As  shown  in  the  figure  the  sHp  is  less  when  the  hnk  is  suspended  at  the  end, 
than  when  suspended  at  the  center.  The  point  of  suspension  is  sometimes 
offset  from  the  Hnk  arc,  the  object  being  to  secure  the  minimum  slip  for 
the  gear  position  in  which  the  engine  is  mostly  run. 

Owes.     When  is  the  slip  greatest  and  least  ? 

Ans.     Greatest  in  full  gear,  and  least  in  mid  gear. 

Owes.     What  conditions  tend  to  reduce  the  slip? 

REVERSE    ROD 

i 


VALVE    STEM 


CENTER 
SUSPENSION 


Fig.  579. — The  Gooch  stationary  link;  used  chiefly  where  the  valve  requires  no  rocker,  as  on 
British  locomotives.  The  lead  is  constant  for  all  cut  offs.  An  abjection  to  the  Gooch  link  is 
that  it  requires  considerable  distance  between  the  shaft  and  cylinder  on  account  of  the  long 
radius  rod  A. 

Ans.     Considerable    angular    advance,     short     travel,    short 
eccentric  rods,  and  a  long  link. 

Owes.     How  long  should  the  link  be  made? 

Ans.     It  ought  to  be  of  such  length  that  its  movement  in 
reversing  is  from  23^^  to  3  times  the  travel  of  the  valve. 


The  Stationary  Link.     Shortly  after  the  appearance  of  the 


LINK  MOTIQNS 


333 


shifting  link  came  the  stationary  Hnk,  also  known  as  the  Gooch 
link,  named  after  its  inventor  Daniel  Gooch.  It  has  been  used 
extensively  on  locomotives  throughout  Great  Britain,  and  the 
continent,  but  is  little  used  on  American  locomotives  as  it  is  not 
adapted  to  engines  having  steam  chests  on  top  the  cylinders; 
it  is  especially  suited  to  engines  having  no  rockers. 


-K* 


Fig.  580. — Stationary  link  motion.  Diagram  for  setting  the  eccentrics  as  given  by  Clark. 
The  eccentrics  must  be  so  placed  as  to  yield  the  necessary  linear  advance  of  the  valve,  or  the 
double  of  it  between  the  positions  of  the  link  at  the  two  ends  of  the  stroke.  Let  X  X',  above 
be  the  center  line,  and  O ,  the  center  of  the  driving  axle.  Through  O,  draw  the  vertical  Y  Y', 
and  describe  the  circle  A,  43^  ins.  in  diameter,  for  the  path  of  the  eccentrics.  Draw  the 
parallels  M,  N,  12  ins.  apart,  equally  distant  from  the  center  line, — the  centers  of  the  link 
being  12  ins.  apart.  On  the  center  O,  with  the  length  of  the  eccentric  rod  as  radius,  which 
in  this  case  is  assumed  for  convenience  at  27  ins.,  or  six  times  the  throw  of  the  eccentrics, 
cut  the  line  M ,  at  T ,  and  draw  TO ,  set  off  O  R  and  O  S ,  each  equal  to  the  linear  advance  of  the 
valve, — 1-^6  ins. — and  draw  the  perpendiculars  RA,  SA",  to  meet  the  circle.  Draw  the  diam- 
eter A  A",  then  OA  and  O  A",are  the  positions  of  the  fore  eccentric  for  the  lead  of  the  in  and  out 
strokes  respectively.  From  A  and  A"  as  centers,  with  the  length  of  the  rod,  cut  the  line  M,  at 
B  and  B",  and  join  AB  and  A"  B".  These  are  the  positions  of  the  fore  eccentric  rod  for  the 
out  and  in  strokes;  and  the  space  BB'',  equal  to  RS,  measures  twice  the  linear  advance  of 
the  valve.  This  construction  is  empirical,  but  it  is  in  ordinary  cases  satisfactory,  and  the 
points  are  easily  adjusted,  if  the  interval  BB'',  be  not  exactly  equal  to  twice  the  linear  ad- 
vance. The  position  of  the  back  eccentric  at  A'  and  A"',  is  found  by  drawing  parallels  to  the 
vertical  Y  Y',  through  the  points  A  and  A".  The  lower  centers  of  the  link,  at  B'  and  B"\  are 
found  similarly  to  the  centers  at  B  and  B''.  Draw  BCB'  and  B",  C  W ,  for  the  relative  posi- 
tions of  the  link.  From  C  and  C,  as  centers,  with  thelength  of  the  sustaining  link  as  radius, 
find  the  point  of  intersection  F,  the  position  of  the  fulcrum,  over  which  the  hnk  will  vibrate 
equally  on  both  sides  of  the  vertical  FD.  The  linear  advance  of  the  eccentrics,  that  is,  the 
perpendicular  distance  of  their  revolving  centers  from  the  vertical  CD,  does  not  exceed 
seven-eighths  inch,  which  is  nevertheless  sufficient,  aided  by  the  obliquity  of  the  rods,  to 
cause  an  advance  of  l^e  ins.  at  the  link.  Applying  the  samemethod  to  find  the  set  of  the 
eccentrics  for  the  54  inch  rods  of  the  valve  motion  already  illustrated,  the  advance  of  the 
eccentrics  is  exactly  1.075  inches,  or  over  IVfe  ins.,  for  I'^g  ins.  of  advance  of  valve.  The 
open  forms  of  link  require  a  like  process  for  the  setting  of  the  eccentrics. 


334 


LINK  MOTIONS 


The  stationary  link  requires  considerable  distance  between  the 
shaft  and  valve  by  reason  of  the  long  radius  rod  necessary  be- 
tween the  link  and  valve  stem.  Its  feature  with  respect  to  the 
steam  distribution  is  that  it  gives  constant  lead  for  all  cut  offs, 
with  either  open  or  crossed  rods. 

The  concave  side  of  the  link  is  turned  toward  the  valve  as  shown  in  fig.  579 
the  radius  of  the  link  being  equal  to  the  length  of  the  radius  rod  A.  To 
reverse  the  engine,  the  block  M,  is  moved  in  the  slot  by  the  lever  C,  and 
reverse  arm  C,  both  keyed  to  the  reverse  shaft  E,  the  movement  being 

REVERSE    ROD 


VALVE 


Fig.  581. — The  Allen  straight  slot  link;    a  modification  of  the  Gooch  link,  and  designed  to 
secure  equal  steam  distribution  at  each  end  of  the  cylinder. 

transmitted  to  the  radius  rod  A,  through  the  reverse  link  L.  The  link  is 
suspended  at  F,  by  the  reach  rod  G,  which  is  pivoted  at  the  fixed  point  H. 
Since  the  radius  of  the  link  is  equal  to  the  length  of  the  radius  rod  A,  it  is 
evident  that  the  block  may  be  shifted  from  one  end  of  the  slot  to  the  other 
without  moving  the  point  S,  therefore  the  lead  remains  constant  for  all 
degrees  of  expansion. 


The  Allen  Link. — This  form  of  Hnk  motion  invented  by 
Alexander  Allen  was  designed  to  combine  the  leading  features 
of  both  the  Stephenson,  and  Gooch  links.     It  is  so  ■  constructed 


LINK  MOTIONS  335 


that  the  parts  are  almost  balanced,  hence  on  locomotives  it  does 
not  require  equalizing  springs,  or  counterweights. 

As  shown  in  fig.  581,  it  consists  of  a  straight  link,  with  a  radius  rod  A, 
and  block  M ;  both  link  and  rod  are  moved  by  a  double  suspension  lever, 
or  rocker  with  arms  C,  C\  attached  to  the  reverse  shaft  E.  Since  the  link 
is  straight,  the  center  of  travel  of  the  block  varies,  but  this  is  compensated 
for  by  the  effect  of  changing  the  slant  of  the  radius  rod  A. 

The  position  of  the  link  and  radius  rod  is  shifted  by  means  of  a  third 
arm  D,  attached  to  the  reverse  shaft  E.  The  proper  proportioning  of  the 
two  arms  C,  C  is  an  irnportant  point  in  the  design  of  this  link  motion. 

Oues.  What  effect  has  the  Allen  link  motion  on  the 
lead? 

Ans.  With  crossed  rods,  the  lead  decreases  as  the  cut  off  is 
shortened. 

Ones.  Is  the  variation  of  lead  greater  with  the  Allen 
or  Stephenson  gear? 

Ans.  With  the  Stephenson  gear;  a  well  proportioned  Allen 
gear,  having  a  long  radius  rod  and  short  travel,  will  give  prac- 
tically constant  lead. 

Ones.     What  are  the  advantages  of  the  Allen  link? 

Ans.  The  parts  being  in  balance  require  no  equalizing  springs 
^or  counterweights ;  the  slip  is  small. 

Oues.     What  disadvantages  does  the  Allen  gear  possess? 

Ans.  It  requires  considerable  distance  between  the  valve 
.and  the  shaft  on  account  of  the  radius  rod.  The  lead  is  constant, 
which  is  not  desirable  for  locomotives.  More  parts  are  required 
than  with  other  types  of  link. 

The  Allen  link  is  specially  adapted  for  use  on  inside  connected  loco- 
motives, that  is,  locomotives  having  steam  chests  at  tne  side  of  the  cylinders 
although  a  modified  form  of  the  Allen  gear  has  been  used  on  American 
locomotives. 


336 


LINK  MOTIONS 


The  Fink  Link, — This  is  a  simple  form  of  link  motion  and 
is  used  on  the  Porter- Allen  engine.  The  lead  is  constant,  and 
its  principles  of  operation  are  illustrated  in  fig.  582. 

The  link  forms  a  part  of  the  eccentric  strap,  and  is  suspended 
at  F,  the  fixed  point  being  below  at  B.  Cut  off  is  varied  by  shift- 
ing the  position  of  the  block  M,  to  which  is  pivoted  the  steam 
radius  rod  D.  The  figure  shows  a  separate  exhaust  radius  rod  D', 


GOVERNOR     ROD 
D' 


EXHAUST    ROD 


Fig.  582.— The  Fink  link;   a  simple  form  of  motion.    Its  special  feature  is  the  long  range  cut 
off,  obtained  without  disturbing  the  motion  of  the  exhaust  valve. 


which  is  set  permanently  in  full  gear;    this  rod  operates  the 
exhaust  valves  independently  of  the  steam  valves. 

Cut  off  is  made  automatic  by  a  connection  G,  to  the  governor. 
When  the  Fink  link  is  used  as  a  reversing  gear,  the  point  of 
suspension  F,  is  placed  at  the  intersection  of  the  line  of  centers, 
and  a  perpendicular  to  it  through  the  center  of  the  link  block 
when  in  full  gear. 


LINK  MOTIONS 


337 


The  link  receives  a  peculiar  motion  on  account  of  the  horizontal  and  the 
vertical  throws  of  the  eccentric.  The  horizontal  throw  alone  only  moves 
it  from  one  to  the  other  of  the  lead  lines,  which  motion  only  draws  off  the 
lap  of  the  valves. 

The  opening  movement  is  produced  by  the  tipping  of  the  link  alter- 
nately in  the  opposite  directions  beyond  the  lead  lines,  these  tipping  motions 
being  given  by  the  vertical  throws  of  the  eccentric. 

The  upward  throw  tips  the  link  in  the  direction  from  the  shaft,  and 
opens  the  port  at  the  further  end  of  the  cylinder;  and  the  downward  throw 
tips  the  link  towards  the  shaft,  and  opens  the  port  at  the  crank  end  of  the 
cylinder.  At  the  same  time  its  horizontal,  throw  is  drawing  the  valve  back, 
and  when,  in  this  return  movement,  that  point  in  the  link  at  v/hich  the  block 
stands,  crosses  the  lead  line,  steam  is  cut  off. 


Figs.  583  and  584.-^Side  and  end  views  of  the  Fink  link  as  constructed  for  the  Porter- Allen 
engine. 


Figs.  583  and  584  show  a  side  and  end  elevation  of  the  Fink 
link  as  designed  for  the  Porter-Allen  engine.  It  should  be  noted 
that  the  link  is  suspended  from  both  sides,  thus  avoiding  any 
lateral  stresses.     The  range  of  cut  off  is  from  zero  to  six-tenths 


338  LINK  MOTIONS 


of  the  stroke.  The  link  is  especially  suited  to  a  long  range  cut  off 
since  the  exhaust  features  are  not  affected  by  the  degree  of 
admission. 

The  exhaust  valves  open  and  close  their  ports  in  such  a  manner  that  the 
opening  is  made  while  the  valve  is  moving  swiftly,  and  one-half  of  the 
opening  movement  has  been  accomplished  when  the  piston  arrives  at  the 
end  of  its  stroke. 

The  valves  are  so  constructed  that  this  portion  of  the  movement  opens 
the  full  area  of  the  port,  which  does  not  begin  to  be  contracted  again  until 
the  center  line  of  the  link  has  recrossed  the  lead  lines  on  its  return.  The 
speed  of  the  piston  is  then  also  diminishing,  and  the  exhaust  is  not  throttled 
at  all  until  the  port  is  just  about  to  be  closed.  By  raising  or  lowering  the 
fixed  point  B,  fig.  582,  the  equality  of  lead,  and  port  openings  in  the  two 
strokes  is  regulated. 

According  to  the  builders  of  the  Porter-Allen  engine,  this  point  should 
be  so  adjusted  that  the  arc  of  motion  at  F,  shall  be  tangent  to  the  center 
line  of  the  engine.  The  motion  of  F,  is  distorted  on  account  of  the  obliquity 
of  the  line  F  E.  To  neutralize  this,  the  makers  use  a  rocker  to  reverse  the 
motion  of  the  valve,  and  put  the  center  of  the  eccentric  on  the  crank  axis. 

The  ratio  of  F  E,  to  O  E,  is  made  the  same  as  the  ratio  of  connecting  rod 
to  crank  so  that  one  error  offsets  the  other,  hence  the  lead  and  cut  off  can 
both  be  equalized. 


RADIAL  VALVE  MOTIONS  339 


CHAPTER  10 

REVERSING  VALVE   GEARS; 
RADIAL   VALVE  MOTIONS 


The  object  sought  in  the  introduction  of  the  so  called  radial 
gears  is  to  overcome  the  defects  of  the  shifting  link  gear,  and  in 
some  cases  to  obtain  a  more  accessible  gear. 

While  the  shifting  link  gives  equal  lead  for  various  cut  offs 
it  does  not  give  constant  lead,  that  is,  as  the  cut  off  is  shortened, 
the  lead  increases  or  diminishes  according  as  the  link  is  arranged 
with  open  or  crossed  rods.  Moreover,  premature  compression 
occurs  as  the  cut  off  is  shortened.  These  distortions  in  the 
steam  distribution  are  in  many  cases  undesirable.  These  de- 
fects, and  the  desire  to  avoid  a  multiplicity  of  eccentrics  on  multi- 
cylinder  engines,  are  the  chief  reasons  for  the  adoption  of  radial 
gears. 

The  better  steam  distribution  secured  by  radial  gears  is  in  some  cases 
more  or  less  offset  by  complicated  construction  consisting  of  numerous 
parts  and  joints  subject  to  wear.* 

General  Principle  of  Radial  Gears. — The  object  sought 
in  the  invention  of  radial  gears  is  to  obtain  from  some  recipro- 
cating or  revolving  piece  oj  the  engine,  an  arrangement  of  mechanism 


*NOTE. — According  to  Sothern  (Principal,  Sothern's  Marine  Engineering  College, 
Glasgow),  the  general  experience  of  engineers  is  that  the  disadvantages  of  radial  gears  more 
than  balance  the  advantages,  with  the  result  that  the  ordinary  link  motion  will  be  found 
fitted  in  even  the  most  modern  and  up  to  date  marine  engines,  as  being  simpler  and  more 
reliable. 


340 


RADIAL  VALVE  MOTIONS 


LAP  +  PORT 

OPENING 


a  point  in  which  shall 
describe  an  oval  curve, 
and  by  altering  the  direc- 
tion of  the  axes  of  this 
curve,  to  produce  variable 
cut  off  and  reversal. 

Accordingly,  a  radial 
gear  may  be  defined  as 
one  in  which  the  motion 
of  the  valve  is  taken  from 
some  point  in  a  vibrating 
rod,  one  end  of  which 
moves  in  a  closed  curve, 
while  a  third  point  on  the 
rod  moves  in  a  straight 
line  or  open  curve. 

Hackworth  Gear. — 

This    gear,    which    was 


HACKWORTH 
GEAR 

Inside  connected  type 
Forward  motion 


ECCENTRIC    ROD  PIVOT 
ECCENTRIC  ROD 
ECCENTRIC 


invented  by 
John  W. 
H  ackworth, 
and  patent- 
ed in  1859. 
and  1876,  was  the 
first  radial  gear  and 
it  probably  gave 
rise  to  all  modem 
radial  gears. 

Fig.  585. — Hackworth  in- 
side connected  valve  gear 
as  constructed  for  a 
marine  engine ;  view  show- 
ing the  various  parts  and 
their  names. 


RADIAL  VALVE  MOTIONS  341 

The  principle  of  the  Hackworth  gear,  as  stated  by  Seaton  is 
as  follows:  ''The  motion  of  a  point  on  a  rod,  one  end  of  which 
moves  in  a  circle,  and  the  other  on  a  straight  line  passing  through 
the  center  of  that  circle,  is  on  an  ellipse  whose  major  axis  coincides 
with  the  straight  line.  If,  however,  the  end  of  the  rod  slide  on  a 
line  inclined  to  this  center  line,  the  major  axis  of  the  ellipse  will 
he  inclined  y 

There  are  two  types  of  Hackworth  gear  which  may  be  clas- 
sified as: 

1.  Inside  connected; 

2.  Outside  connected; 

according  as  the  valve  rod  is  connected  to  the  eccentric  rod 
between  the  eccentric  and  eccentric  rod  pivot,  or  beyond  the 
eccentric  rod  pivot. 

Fig.  585  shows  the  inside  connected  type  as  arranged  for  outside  ad- 
mission. Its  essential  parts  are:  eccentric,  eccentric  rod,  link,  valve  rod, 
eccentric  rod  pivot,  link  pivot,  and  valve  rod  pivot,  and  means  for  shifting 
and  securing  the  link  in  any  position  within  its  arc  of  adjustment.  As 
shown,  the  center  of  the  eccentric  is  at  E,  or  opposite  the  crank,  corre- 
sponding to  90  degrees  angular  advance. 

The  link  consists  of  a  straight  slot  and  guides  a  reciprocating  block 
which  is  pivoted  to  the  end  of  the  eccentric  rod  at  F.  The  pivot  L,  of  the 
link  is  located  in  the  line  X  X',  which  passes  throllgh  the  center  of  the 
shaft  perpendicular  to  the  cylinder  axis  Y  Y'.  The  point  of  cut  off  and 
direction  of  rotation  of  the  engine  depend  upon  the  angular  position  of  the 
link  witji  respect  to  the  axis  X  X'. 

The  location  of  pivot  L,  and  length  E  B,  of  the  eccentric  rod  is  such 
that  E  B  =E'  L.  When  these  two  distances  are  equal,  F,  will  coincide  with 
the  center  L,  of  the  link  when  the  connecting  rod  is  on  either  dead  center, 
and  the  slotted  link  may  be  turned  from  full  gear  forward  through  its 
horizontal  position  to  full  gear  reverse  without  moving  the  valve.  Hence, 
when  the  lap  is  the  same  on  both  ends  of  the  valve  the  leads  are  constant 
for  all  positions  of  the  link,  and  consequently  for  all  cut  off. 

The  valve  is  set  by  adjusting  the  valve  stem  for  equal  lead. 

The  correct  location  of  the  valve  rod  pivot  V,  is  necessary  to  secure 
proper  steam  distribution.    V,  must  be  so  located  that  when  the  engine  is 


342 


RADIAL  VALVE  MOTIONS 


LAP  +  LEAD 


on  the  dead  center  and  the  link  is 
in  its  horizontal  position  the  distance 
from  V  to  the  horizontal  axis  X  X' 
=  lap-\-leadf  as  shown  in  fig.  586. 

The  operation  of  the  gear  may 
perhaps  be  better  presented  graph- 
ically than  by  description.  Thus, 
figs.  587  to  5iO  show  the  positions 
of  the  gear  in  full  forward  motion 
for  the  principal  events  of  the  stroke, 
viz.:  lead,  cut  off,  pre-release,  and 
compression,  and  figs.  591  to  594 
similar  positions  in  full  reverse 
motion. 

Figs.  595  to  597  show  the  gear 
in  full  forward  motion  for  various 
inclinations  of  the  link  giving  various 
cuts  off. 

In  addition  to  permitting  re- 
versal with  only  one  eccentric, 
the  chief  advantages  of  this  gear 
are  its  quick  motion  at  the  point 
of  cut  off  and  the  large  range 
of  cut  off  possible,  wire  drawing 
from    small    opening    and    slow 
closing  of  the  port,    as   is    the 
case     with     the     shifting     link 
motion. 
The  chief  objec- 
tions   to   Hack- 
worth's  gear  are: 
1.  The  friction  and 
wear  of  the  block  and 
link  especially    when 
the  link  is  inclined  to 
the  XX'  axis; 


Fig.  586. — Hackworth  gear  at  dead  center  p»sition  showing  that 
the  valve  rod  pivot  V,  must  be  so  located  on  the  eccentric  rod 
that  its  distance  from  the  horizontal  axis  X  X'  =  lap  -\-lead.    This 
must  be  evident,  because  the  valve  as  shown  in  section  must  have  its  proper  linear  advance. 


HACKWORTH  GEAR 

Forward  motion 
Inside  connected  type 


PATH  OF  PIVOT  V 
LAP  +  LEAD 


RADIAL  VALVE  MOTIONS 


343 


UT  OFF 


COMPRESSION 


Figs.  587  to  590. — Hackworth  gear  at  positions  of  lead,  cut  off,  pre-release,  and  compression 
for  forward  full  gear  motion. 


344 


RADIAL  VALVE  MOTIONS 


UT  OFF 


COMPRESSION 


Pigs.  591  to  594. — Hackworth  gear  at  positions  of  lead,  cut  off;  pre-release,  and  compression, 
for  reverse  full  gear  motion. 


RADIAL  VALVE  MOTIONS 


345 


HACKWORTH  GEAR 

Various  cut  offs;  forward  motion 


Figs.  595  to  597. — Hackworth  gear  at  various 
cut  off  positions  forward  motion. 


346 


RADIAL  VALVE  MOTIONS 


OUTSIDE  CONNECTED 


HACKWORTH  GEAR 

Inside  and  outside  connected  types 
Forward  motion 

INSIDE  ADMISSION 

LAP  +  LEAD 


Fig.  598. — ^Hackworth  inside  connected 
gear  as  arranged  for  inside  admission 
valve. 


Figs.  599  and  600. — Hackworth  out- 
side connected  gear;  fig.  599,  as 
arranged  for  outside  admission  valve; 
fig.  600,  as  arranged  for  inside  ad- 
mission valve. 


OUTSIDE  CONNECTED 


RADIAL  VALVE  MOTIONS 


347 


2.  Large  eccentric  necessary 
when  valve  rod  pivot  is  located 
between  the  eccentric  and 
eccentric  rod  pivot; 

3.  Considerable  traverse 
stress  on  the  eccentric  when 
the  valve  is  unbalanced; 

4.  Numerous  pins,  liable  to 
derangement. 

In  later  designs  the  first  objec- 
tion was  overcome  by  using  rollers 
instead  of  a  sliding  block.  The 
gear  has  worked  fairly  well,  and  for 
engines  of  small  power  has  been 
found  a  convenient  arrangement, 
especially  when  much  variation  in 
cut  off  is  required. 

Fig.  598  shows  the  inside  con- 
nected gear  arranged  for  inside 
admission.  Here  the  eccentric  is  in 
line  with  the  crank,  180°  from  its 
position  for  outside  admission,  that 
is,  its  angular  advance  is  made — 
90°  instead  of  +90°.  Figs.  599 
and  600  show  the  outside  connected 
gear  arranged  respectively  for  out- 
side and  inside  admission. 


HACKWORTH   GEAR 

Inside  connected  type 
Reverse  motion 


Pig.   601. — Hackworth  inside   connected   gear   as   arranged   with 
vertical  eccentric  rod. 


348 


RADIAL  VALVE  MOTIONS 


LAP  +  LEAD  Since  several  of   the  modern 

radial  gears  are  simply  modi- 
fications of  the  Hackworth  gear, 
the  latter  has  been  presented  at 
some  length  in  order  to  fully 
illustrate  underlying  principles 
rather  than  mechanical  con- 
struction, as  it  has  largely  been 
replaced  by  the  more  modem 
forms  because  of  mechanical 
difficulties. 


Gear. — This  first 
modification 
of  the  Hack- 
worth  gear, 
due  to  F.  C. 
Marshall, 
was  intro- 
du  ced  to 
overcome  the 
chief  defect  of 
the  H  ack- 
worth  gear, 
that  is  the 
wear  and 
friction  of  the 
sliding  block. 
LAP  +  lead' 

Fig.  602. — Marshall  gear,  or  first  modification  of  the  Hackworth 
gear. 


RADIAL  VALVE  MOTIONS 


.349 


It  is  simply  the  Hackworth  gear  with  a  swinging  arm  substi- 
tuted for  the  link  as  shown  in  figs.  602  and  603,  the  other  parts 
are  exactly  as  Hackworth  arranged  them. 

Here  the  eccentric  rod  pivot  F,  located  at  the  end  of  the  rod  is  attached 
to  a  suspension  or  radius  rod  R,  the  other  end  of  which  is  pivoted  at  P,  to 
a  radius  arm  R',  which  turns  about  L,  and  whose  angular  position  with 
respect  to  the  central  axis  y  y\  controls  the  point  of  cut  off  and  direction 
or  rotation.  In  construction,  a  geared  quadrant  is  attached  to  the  radius 
arm  to  provide  means  for  setting  the  radius  arm  in  any  position  within 
its  arc  of  adjustment.  v 


CENTER  OF 
ECCENTRIC 


RADIUS 
ROO^ 


Fig.  603. — Construction  detail  of  Marshall  valve  gear  showing  general  proportion  of  parts. 

The  pivot  L,  is  located  precisely  as  in  the  Hackworth  gear. 

Since  P  P,  is  made  equal  to  P  L,  the  arc  described  by  F,  will  pass  through 
L,  for  all  angular  positions  of  the  radius  arm,  and  P,  will  coincide  with  L, 
when  the  engine  is  on  either  dead  center.  Hence,  if  the  laps  be  the  same 
the  lead  will  be  constant  and  equal. 

The  motion  of  the  valve  is  the  resultant  of  the  two  vertical  components 
of  motion  due  to  the  eccentric  and  radius  arms  acting  at  the  ends  of  the 
eccentric  rod. 
.  The  steam  distribution  of  the  Marshall  gear  is  not  so  good  as  with  the 


350 


RADIAL  VALVE  MOTIONS 


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RADIAL  VALVE  MOTIONS 


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RADIAL  VALVE  MOTIONS 


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RADIAL  VALVE  MOTIONS 


353 


connected,  or  pivoted  to  the  end 
instead  of  the  middle  of  the  ec- 
centric rod. 

The  gear,  as  constructed  for .  a 
marine  engine  is  shown  in  fig.  610, 
and  consists  of  a  single  eccentric  E, 
which  either  has  to  be  set  directly 
opposite  the  crank  C,  or  in  the  same 
direction  with  the  crank,  according 
to  the  design  of  the  valve  gear. 

The  eccentric  operates  the  eccen- 
tric rod  L,  which  also  forms  one- 
half  of  the  eccentric  strap  J,  the 
extreme  en4  of  this  lever  is  attached 
to  the  valve  rod,  by  means  of  a 
pivot  N,  and  thus  to  the  valve 
stem.  ■  . 

The  fulcrum  of  the  eccentric  rod 
is  at  F,  about  which  it  is  swuug 
vertically  by  the  throw  of  the 
eccentric,  the  amount  of  travel  thus 
imparted  to  the  valve  being  equal  to 
the  lap  and  lead  for  both  ports. 

The  travel  necessary  to  open  the 
port  is  imparted  to  the  valve  through 
port  N ,  by  the  up  and  down  motion 
of  the  fulcrum  F,  due  to  the  horizon- 
tal throw  of  the   eccentric,  which 
causes       the 
radius    rod    R, 
pivoted  at  K,  to 
swing,  and  thus 
raise  and  lower 
the  fulcnim. 


BREMME  GEAR 

Forward  motion 


ADIUS  ARM 

R' 
RADIOS  ROD 

OUTSIDE  CONNECTED  _ 
CCENTRIC  ROD  PIVOT 


Fig.  610. — Bremme 
gear,  or  second 
modification  of 
the  Hackworth 
gear. 


LAP  +  LEAD 


354 


RADIAL  VALVE  MOTIONS 


The  upper  end  of  the  radius  rod  R,  is  pivoted  to  the  radius  arm  R',  which 
can  be  swung  about  the  pin  F,  by  means  of  the  reversing  gear,  which 
is  similar  to  that  shown  in  fig.  603,  the  construction  being  explained  in 
the  accompanying  text. 


BREMME   GEAR 

Various  cut  offs;  forward  motion 

Pig.  611. — Bremme  gear  in  cut  off  position  for  latest  cut  off;   forward  gear. 
Fig.  612. — Bremme  gear  in  cut  off  position  for  short  cut  off;   forward  gear. 

It  rnust  be  understood  that  when  the  radius  arm  R'  (sometimes,  though 
ill-advisedly  called  tumbling  link*)  is  at  its  midway  position,  no  vertical 
motion  is  given  to  the  fulcrum  F,  and  if  it  be  thrown  over  into  its  opposite 

*NOTE. — The  author  prefers  to  confine  the  word  link  to  mean  a  slotted  bar  or  device 
wherein  a  block  slides  as  in  the  shifting  or  so  called  Stevens  link. 


RADIAL  /ALVE  MOTIONS  355 

position  the  motion  is  reversed  to  that  indicated  in  the  figure.    By  reducing 
the  incHnation  of  the  arm,  the  cut  off  is  shortened. 

According  to  the  inventor,  the  angle  of  the  reversing  lever  (that  is,  the 
radius  arm  R',  fig.  608)  from  the  central  line  and  known  as  the  "deviation 
line"  should  never  exceed  25°  on  either  side. 

Joy   Gear. — This  gear  invented  by  David  Joy  in   1880  is 

perhaps  the  best  known  of  the  radial  gears,  and  avoids  altogether 
the  use  of  eccentrics.  Its  motion  is  superior  to  that  of  the  or- 
dinary eccentric  in  that  the  parts  are  opened  and  closed  rapidly 
with  slow  valve  movement  during  expansion  and  exhaust. 

The  lead  is  constant,  and  the  cut  off  nearly  equalized  for  all 
grades  of  expansion.  The  compression  is  less  at  short  cut  off 
than  with  link  motion. 

The  Joy  gear  has  been  extensively  used  on  English  locomotives 
and  on  marine  engines. 

The  chief  objections  to  the  gear  are  its  great  number  of  parts 
and  joints  which  are  in  the  way  and  subject  to  wear.  In  design 
the  various  pins  should  be  made  substantial. 

In  the  Joy  gear  motion  is  obtained  from  the  connecting  rod 
and  imparted  to  one  end  of  what  corresponds  to  the  eccentric 
rod  in  the  previous  gears,  the  other  end  of  which  is  connected 
to  the  valve  rod.  There  are  two  types  of  Joy  gear,  classified 
according  as  the  motion  received'  from  the  connecting  rod  is 
modified  by: 

1.  A  link; 

As  in  the  Hackworth  gear,  or 

2.  Radius  rod 

as  in  the  Bremme  gear. 

Fig.  613  shows  the  link  type  as  applied  to  a  marine  engine. 

The  lever  A,  (previously  mentioned  as  corresponding  to  the  eccentric 
rod  in  the  radial  gears  already  described,  especially  the  Bremme  gear),  is 
pivoted  at  B,  to  a  block  arranged  to  slide  in  the  curved  link  L,  the  pivot 
forming  the  fulcrum  of  the  lever  A- 


356 


RADIAL  VALVE  MOTIONS 


Motion  is  imparted  to  the  lever  A,  directly  from  the  connecting  rod  by 
means  of  the  rod  C,  one  end  of  which  is  pivoted  to  the  connecting  rod,  the 
other  end  to  the  rod  D. 

The  vertical  motion  of  the  rod  C,  moves  the  valve  an  amount  equal  to 
its  lap  +  lead,  while  the  horizontal  motion  causes  the  ports  to  open  their 
full  opening  by  moving  the    fulcrum  up  and  down  in  the  inclined  link. 


Fig.  613.— Joy  valve  gear,  link  type.     In  this  gear,  as  can  be  seen,  no  eccentric  is  employed, 
the  motion  being  taken  from  the  connecting  rod,  thus  permitting  more  liberal  main  bearings. 


By  means  of  the  reversing  lever  R,  the  inclination  of  the  link  L,  can  be 
altered,  or  reversed,  to  vary  the  cut  off  or  reverse  the  engine. 

Fig.  614  shows  the  radius  rod  type  of  Joy  gear  as  applied  to  a  marine 
engine. 


RADIAL  VALVE  MOTIONS 


357 


Diagram  for  Setting  Out  Joy's  Valve  Gear. — The  following 
is  the  method  of  design  as  given  by  the  inventor: 

"On  the  connecting  rod  AB,  fig.  615,  take  a  point  C,  so  that  its  total 
vertical  vibration  DD',  is  not  less  than  twice  the  full  valve  travel, 
perferably   a   little  more.     Through    DD',  draw    XX,  perpendicular  to 


RADIUS 
ROD 


Fig.  614.— Joy  valve  gear,  radius  rod  type.    The  substituting  of  a  radius  rod  in  place  of  the 
link  avoids  the  objectional  friction  and  wear  of  the  latter. 


AB,  and  at  the  proper  distance  from  AB,  lay  down  the  center  line  of  the 
valve  spindle.  Mark  the  extrerne  position  of  the  point  C,  for  inner  and 
outer  dead  centers,  and  choose  such  a  lever  CE,  whose  total  angle  of  vibra- 
tion CEC,  does  not  exceed  90°,  and  carry  the  end  E,  by  an  anchor  link 


358 


RADIAL  VALVE  MOTIONS 


E  F,  the  mid  position  of 
which  is  parallel  to  the 
connecting  rod  when 
horizontal. 

''Next,  on  the  center 
line  of  the  valve  spindle 
produced,  and  on  each 
side  of  the  vertical  X  X, 
mark  off  the  points  J  J', 
each  distant  from  the 
vertical  by  an  amount 
equal  to  lap  and  lead. 
From  the  point  J,  draw 
a  line  J  H,  the  center 
line  of  a  link  that,  by 
virtue  of  its  connection 
to  C  E,  will  move  the 
point  K  (the  point 
where  J  H  crosses  the 
vertical)  equally  o  n 
each  side  of  the  central 
point  K.  The  point  K, 
is  the  center  of  oscil- 
lation of  the  curved 
guides  in  which  slide  the 
blocks  carrying  the  ful- 
crum M,  of  thelever  JH. 
The  position  of  H,  is  best 
found  by  a  tentative 
process,  and  to  test 
whether  the  chosen  point 
be  a  correct  one,  the 
equal  vibration  required 
is  marked  off  on  each  side 
of  K,  and  lettered  L  L. 
The  distance  LL,  is  equal 
to  the  vertical  vibration 
of  the  point  C,  on  the 
connecting  rod,  that  is 
DD'.  From  D,  as  center, 
and  with  C  H,  as  radius, 
mark  the  point  M,  on  the 
vertical  X  X,  and  with 
the  same  radius,  mark 
off  N,  from  D',  M  and 
N,  are  the  positions  of 
H,  when  the  engine  is  at 


RADIAL  VALVE  MOTIONS  359 


half  stroke,   or  thereabouts,    and    these   points   give    the    total    vertical 
vibration  of  H. 

"From  M,  as  center,  and  with  HK,  as  radius,  describe  an  arc  cutting 
the  vertical  XX,  and  from  N,  as  center  and  with  the  same  radius  describe 
an  arc  also  cutting  the  vertical  XX,  then,  if  the  point  H,  be  the  correct  one, 
the  arcs  just  drawn  cut  the  vertical  XX,  at  L  and  L.  Should  the  points- 
of  intersection  fall  helow  L  and  L,  H  is  too  near  E,  but  if  they  fall  above  L 
and  L,  H  is  too  near  C.  The  exact  position  of  H,  is  generally  found  by  a 
second  trial.  The  valve  rod  JG,  may  be  of  any  convenient  length,  but 
the  center  line  of  the  slides  must  be  struck  with  the  same  radius.  From 
the  point  K,  draw  a  line  KO,  parallel  to  AB,  and  with  center  on  this,  line, 
and  with  JG,  as  radius,  describe  an  arc  containing  K,  and  cutting  the: 
curves  LL,  struck  from  K,  as  center,  in  PP'. 

"From  P,  or  P',  and  on  each  side  thereof,  mark  off  on  the  arcs  LL,  an 
amount  equal  to  IJ^  times  the  maximum  port  opening  required,  and  let 
RR',  be  the  points.  With  centers  on  the  arc  SS,  struck  from  center  K,. 
describe  arcs  passing  through  K  R  and  K  R',  these  arcs  represent  the  center 
lines  of  the  curved  slots  for  forward  and  backward  gear,  and  when  the: 
latter  are  in  either  of  these  positions  the  point  of  cut  off  is  about  75%. 
Should  a  later  cut  off  be  required  the  slots  must  be  carried  still  further 
from  their  vertical  position. 

"It  is  seen  in  the  diagram  that  the  fulcrum  K,  of  the  lever  JH,  coincides 
with  the  center  of  oscillation  of  the  curved  slots  or  guides  when  the  crank 
is  on  either  dead  center.  Evidently  when  these  points  coincide,  the  angle 
of  the  guide  can  be  altered  to  any  extent  without  disturbing  any  other 
part  of  the  mechanism,  a  state  of  things  which  shows  that  the  lead  is. 
constant." 

The  inventor's  pamphlet  goes  on  to  say  that  when  the  above  directions- 
are  followed,  the  leads  and  cut  offs  for  each  end  of  the  cylinder  for  back- 
ward and  forward  gear  are  practically  equal. 

The  arrangement  of  the  gear  just  described  is  the  most  effective  but 
considerable  latitude  is  permissible.  For  instance  the  point  C,  can  be 
placed  above  or  below  the  center  line  of  the  connecting  rod  and  the  point  K, 
can  be  raised  or  lowered,  so  that  the  line  KO,  is  no  longer  parallel  to  AB, 
but  it  is"  not  advisable  that  the  line  should  have  a  greater  inclination  to- 
AB,  than  4°  or  thereabouts. 

Again,  the  anchor  link  may  be  dispensed  with,  the  point  J,  being  guided 
in  a  slide  affixed  to  some  convenient  part  of  the  engine.  For  vertical 
engines  the  same  rules  apply  by  placing  the  diagram  vertically  and  altering, 
relatively  the  terms  vertical  and  horizontal. 


Joy  and   Bremnie   Gears   Compared. — The  Joy   gear  is 
preferred  for  locomotives,  and  the  Bremme  for  marine  engines. 


360 


RADIAL  VALVE  MOTIONS 


It  is  somewhat  difficult  to  arrange  the  Bremme  gear  with  its  eccentric 
rod  and  reversing  arm  underneath  a  locomotive  boiler,  so  as  to  be  compact, 
and  to  clear  the  various  parts.  In  marine  work,  space  for  this  is  usually 
abundant.  The  movement  of  the  parts  of  the  Bremme  gear  is  considerably 
less  than  the  Joy. 


ECCENTRIC 
ROD 


LINK 


VALVE  ROD 


VALVE 
5TEM 


^^#»^W 


COMNECTING 
■       ROD 


A       GOMBINATJON 
REVERSING  LEVER 

SHAFT 


Fig.  616. — Walschaerts  valve  gear  as  applied  to  a  locomotive. 


Walschaert  Gear. — This  type  of  valve  motion  is  one  of  the 
most  important  of  the  so  called  radial  gears. 

It  was  invented  by  Egide  Walschaerts*  (incorrectly  spelled  Walschaert, 
Walschart,  etc.),  of  Mechlin,  near  Brussels,  Belgium,  and  is  especially 
adapted  to  locomotives. 


*^0T^.— Egide  Walschaerts  died  on  Xha  18th  of  February,  1901,  at  Saint- Gilles,  near 
Brussels,  at  the  age  of  eighty-one  years.  His  mechanism  which  is  so  original,  has  been  adopted 
for  rnany  years  in  most  of  the  countries  of  Europe  and  has  been  wrongly  attributed  to  Mr. 
Huesinger  von  Waldegg.  He  was  born  Janusry  21,  1820,  at  Malines,  which  place  became, 
fifteen  years  later,  the  central  point  of  the  system  of  Belgian  Railways.  The  line  from  Brus- 
sels to  Malines  was  opened  in  18;:55,  and  this  event  decided  the  career  of  young  Walschaerts. 
Three  years  later,  at  the  exhibition  of  products  of  Malines,  there  appeared  some  remarkable 
models  executed  by  him,  and  described  as  follows  in  the  catalogue:  No.  19.  M.  E.  Wals- 
chaerts, Jr.,  student  of  the  Municipal  College:  {a)  A  stationary  steam  engine  of  iron  (the  main 
piston  having  the  diameter  of  4 .5  cm,  or  1 .77  in.)  (&)  A  working  model  of  a  locomotive  in  copper 
to  the  scale  of  V20  of  the  railway  locomotives,  (c)  Section  of  a  stationary  steam  engine. 
{d)  Model  of  a  suction  pump  and  a  duplex  pump,  (g)  Glass  model  of  an  inclined  plane.  Min- 
ister Rogier  was  so  much  struck  by  it  that  he  had  Walschaerts  enter  the  University  of  Liege, 
but  his  studies  were  interrupted  by  a  serious  illness,  and  were  never  completed.  We  find 
traces  of  him  at  the  National  Exhibition  in  Brussels  in  1841.  The  report  of  the  jury  men- 
tions with  praise  a  small  locomotive  constructed  entirely  by  Walschaerts,  and  a  steamboat 
6.50  metres  long  and  1.75  metres  wide,  which  was  capable  of  carrying  sixteen  men  and  travel- 
ing (so  the  report  says)  at  four  leagues  an  hour  on  the  canal.  The  boiler  of  this  little  boat 
was  of  a  new  system  invented  by  the  constructor.  The  jury  does  not  give  further  details. 
Walschaerts  received  the  silver  medal.  In  1842  Walschaerts  was  taken  into  the  shops  of  the 
State  Railway  at  Malines  as  a  mechanic.  Machine  tools  existed  only  in  the  most  rudimentary, 
forms,  and  the  store  rooms  were  badly  provisioned.     The  lack  of  organization  in  the  shops 


RADIAL  VALVE  MOTIONS 


36t 


The  recent  development  of  the  locomotive  in  this  eoimtry  has  presented 
conditions  that  has  caused  the  extensive  use  of  the  Walsbh^erts 'gear  in 
place  of  the  shifting  link ^  '        -  ,    -/  .   .  : 

The  Walschaerts  gear  like  other  radial  gears  gives  a  constant  lead  and 
cannot  be  adjusted  without  disturbing  the  other  events.     ^  /    - 

The  layout  of  this  gear  is  more  or  less  a  matter  of  trial,  many  minor 


Fig.  617. — Skeleton  diagram  of  Walschaerts  valve  gear.  In  operation,  the  movement  given 
to  the  valve  slide  A,  is  the  resultant  of  two  components.    The  first  is  derived  from  the  eccen- 

■  trie  E,  through  the  link  L,  and  varies  in  amount  as  B,  is  moved  out  from  P,  and  in  direction 
relative  to  the  crank  as  B  is  above  or  below  P.  The  second  component  is  derived  from  the 
cross  head  through  the  combination  lever  C.  The  resultant  effect  is  equivalent  to  the  motion 
that  would  be  given  by  a  single  eccentric  shifting  along  a  straight  line. 

locations  may  be  varied  in  design,  such  as  the  position  of  the  link  pivot^or 
the  point  where  the  eccentric  rod  is  pivoted  to  the  link,  and  in  this  way 
modifications  in  the  action  of  the  valve  may  be  accomplished. 


l^OT^.— Continued, 
rendered  a  man  of  Walschaerts  abilities  particularly  valuable,  and  at  the  end  of  two  years 
he  was  made  shop  foreman  at  Brussels.  Although  he  was  only  twenty-four  years  of  age  he 
had  already  shown  the  qualities  which  make  an  engineer,  which  should  have  carried  him  in 
a  few  years  to  be  the  technical-  head  of  the  motive  power  department.  It  is  humihating  to 
be  compelled  to  say  that  he  remained  shop  foreman  throughout  his  life.  The  first  locomotive 
came  from  England  and  had  not  been  in  service  for  more  than  ten  years  when  Walschaerts 
was  made  foreman.  The  railroad  was  growing  rapidly  and  it  was  necessary  to  increase  the 
forces  and  to  acquire  experience.  Walschaerts  was  not  content  with  the  duties  incurred  in 
these  difficult  circumstances,  but  began  his  career  by  the  invention  of  his  system  of  valve 
motion.  On  October  5,  1844,  Mr.  Fischer,  Engineer  of  the  Belgian  State  Railwa^j-'s,  filed 
for  Egide  Walschaerts  an  application  for  a  patent  relating  to  a  new  system  of  steam 
distribution  applicable  to  stationary  steam  engines  and  to  locomotives.  The  Belgian  patent 
was  issued  on  November  30,  1844,  for  a  term  of  fifteen  years.  The  rules  of  the  department  did 
not  allow  a  foreman  to  exploit  a  Belgian  patent  for  his  own  profit  and  this  explains  probably 
the  intervention  of  Mr.  Fischer,  who  has  never  claimed  the  slightest  part,  material  or  moral 
of  the  invention.  On  October  25th  of  the  same  year,  Walschaerts  took  out  a  patent  in  France 
for  the  same  invention.  There  also  exists  among  the  documents  left  by  the  inventor,  a  con- 
tract signed  at  Brussels  in  1845  by  Demeuldre,  from  which  it  appears  that  he  undertook  to 
obtain  a  patent  of  importation  into  Prussia  for  the  new  valve  motion,  subject  to  an  assignment 
by  Walschaerts  of  half  of  the  profits  to  be  deducted  from  the  introduction  of  the  new- 
valve  motion  in  this  country.  It  is  probable,  however,  that  this  contract  was  never  carried 
out.  The  design  attached  to  the  Belgian  patent  is  a  primitive  arrangement,  the  link  oscil- 
lated on  a  fixed  shaft,   in  regard   to   which  it   was  symmetrical,   but   it   had   an  enlarged 


362  RADIAL  VALVE  MOTIONS 

In  the  chapter  on  locomotives,  the  Walschaerts  gear  is  de- 
scribed in  detail,  hence  only  an  outline  of  its  working  princi- 
ples need  be  given  here. 

The  essential  features  of  the  gear  are  shown  in  fig.  617. 

The  motion  of  the  valve  is  the  resultant  of  two  movements,  one  of  which 
is  intended  to  give  constant  lead,  and  the  other,  the  required  travel  of  the 
valve.  These  two  movements  are  due  to  the  cross  head  and  eccentric, 
and  are  combined  and  imparted  to  the  valve  by  the  combination  lever  as 
shown  in  fig.  616. 

Motion  from  the  cross  head  is  delivered  to  the  lower  end  of  the  com- 
bination lever  by  a  stud  bar  A,  fixed  to  the  cross  head  and  rod  B,  giving 
it  a  reciprocating  motion  equal  to  the  length  of  the  stroke. 

The  second  movement  is  transmitted  from  the  eccentric  through  the 
eccentric  rod,  link  pivoted  at  B,  and  valve  rod  (sometimes  called  radius 
rod),  to  the  combination  rod. 

The  valve  rod  is  pivoted  to  the  combination  rod  at  a  point  C,  near  its 
upper  end,  so  located  that  the  motion  received  from  the  cross  head  will 
reciprocate  the  valve  stem  through  a  space  equal  to  twice  the  linear  ad- 
vance, and  thus  to  place  the  valve  in  position  with  constant  lead  at  the 
beginning  of  the  stroke. 

The  link  is  curved  to  a  radius  equal  to  the  length  of  the  valve  rod.  The 
valve  rod  has  a  block  pivoted  near  its  end,  and  arranged  to  slide  in  the  link 
as  shown. 

The  cut  off  is  shortened,  or  motion  reversed  by  shifting  the  block  by 
means  of  the  reverse  crank  and  reach  rod  which  joins  this  crank  to  the 
end  of  the  valve  rod. 


l^OT'E— Continued. 
opening  at  the  center  so  that  only  at  the  ends  was  it  operated  without  play  by  the  link  blocks 
which  was  made  in  the  form  of  a  simple  pin.  There  was  only' one  eccentric,  the  rod  of  which 
terminated  in  a  short  T,  carrying  two  pins.  The  reverse  shaft  operated  the  eccentric  rod  and 
maintained  it  at  the  desired  height.  For  one  direction  the  lower  pin  of  the  T  engaged  in  the 
lower  end  of  the  link,  and  to  reverse  the  engine  the  rod  was  raised  so  that  the  upper  pin  engaged 
in  the  upper  end  of  the  link.  The  angle  of  oscillation  of  the  link  varied  with  the  position 
of  the  pin  in  the  link,  and  this  oscillation  was  transmitted  by  an  arm  to  the  combining  lever, 
which  was  also  operated  by  the  cross  head.  The  central  part  of  the  link  could  not  be  used 
for  the  steam  distribution,  as  it  was  necessary  to  enlarge  it  to  allow  for  the  play  of  the  pin 
which  was  not  in  operation .  It  may  be  asked  why  the  inventor  used  two  separate  pins  mounted 
on  a  cross  piece  on  the  end  of  the  eccentric  rod,  instead  of  a  single  pin  on  the  center  of  the 
rod  which  would  have  served  for  both  forward  and  backward  motion  without  requiring  the 
center  enlargement  of  the  link.  It  must  be  borne  in  mind  that  the  raising  or  lowering  of  the 
eccentric  rod  by  the  reverse  shaft  was  equivalent  to  a  slight  change  in  the  angular  advance 
of  the  eccentric.  Consequently  with  a  link  of  a  sufficient  length  to  keep  down  the  effect  of 
the  angularity  it  was  necessary  to  reduce  as  much  as  possible  the  movement  of  the  eccentric 
rod.  ■  Notwithstanding  its  differences  the  mechanism  described  in  the  patent  of  1844  is  in 
principle  similar  to  the  valve  motion  with  which  every  one  is  to-day  familiar  and  which  the 
inventor  constructed  as  early  as  1848,  as  is  shown  by  a  drawing  taken  from  the  records  of  the 
Brussels  shops,  on  which  appears  the  inscription  "Variable  expansion;  E.  Walschaerts  system 
applied  to  Locomotive  No.  98,  Brussels,  September  2,  1848." 


GOVERNORS  363 


CHAPTER  11 
GOVERNORS 


An  important  requirement  of  engine  operation  for  mOst 
conditions  of  service  is  the  maintenance  of  ,a  practically  constant 
speed  under  variable  load.  This  control  is  accomplished  by  an 
automatic  device  called  a  governor.  With  respect  to  speed 
control,  engines  may  be  divided  into  two  general  classes,  ac- 
cording as  they  are  designed  to  run  at 

1.  *  Variable  speed,  or 

2.  *   Constant  speed. 

The  speed  regulation  of  the  two  types  is  classed  respectively  as 

1.  Hand  control; 

2.  Automatic. 

Under  the  first  division'  are  types  such  as  marine,  locomotive,  and 
hoisting  engines,  while  the  second  division  consists  of  that  lar^e  class 
known  as  stationary  engines. 

Classes  of  Governor. — The  varied  conditions  of  service  give 
rise  to  numerous  types  of  governor  differing  bo'th  in  principle 
and  construction.     Accordingly,  governors  may  be  classed: 


♦NOTE. — It  should  be  understood  that  there  is  a  type  o.  engine  called  "variable  speed 
engine,"  which  works  under  control  of  a  governor  so  arranged  that  the  speed  may  be  altered 
as  fully  explained  on  page  398. 


364  GOVERNORS 


1.  With  respect  to  steam  control  as 

a.  Throttling; 

h.  Variable  cut  off. 

2.  With  respect  to  the  operating  principle,  as 


a.  Centrifugal  I  f-J,^^^' 
h.  Inertia. 

3.  With  respect  to  operation,  as 

a.  Sensitive; 

b.  Isochronous; 

c.  Variable  speed. 

4.  With  respect  to  construction,  as 

a.  Pendulum     {}J,^^^-f^^ 

(shifting  eccentric; 
swinging  eccentric; 
double  eccentric. 

Principle  of  Centrifugal  Governor. — The  action  of 
governors  of  the  type  depends  upon  the  change  of  centrifugal 
force  when  the  rate  of  rotation  changes. 

In  these  governors  one  of  two  resisting  forces  is  employed 
as  that  due  to  gravity,  or  a  spring.  Gravity  is  usually  the 
resisting  force  in  pendulum  governors,  and  one  or  more  springs 
in  shaft  governors. 

In  fig.  618  le^ 

h   =  height  of  cone  of  revolution; 

r    =  radius  of  rotation  of  ball; 

W  =  weight  of  ball ; 

C  =  centrifugal  force  due  to  speed  of  rotation 

then 


GOVERNORS 


365 


from  which 


W  = 


Ch 


C  = 


Wr 


Ch_ 


h  = 


Wr 


Ques.  Upon  what  does  h,  or  distance  of  the  plane  of 
the  ball  below  the  point  of  suspension  (popularly  expressed 
as  ''height  of  the  ball")  depend? 

Ans.  The  distance  h  varies  inversely  as  the  square  of  the 
speed. 

The  weight  of  the  ball  and  radius  of  revolution  have  no  effect  upon  the 
position  of  the  balls. 


POJMT   OF^ 
SUSPENSION 


CENTRIFUGAL 
PORCE 


RADIUS  OF 
ROTATION 

Fig.  618. — Simple  revolving  pendulum  illustrating  the  principle  of  operations  of  centrifugal 
governors. 

Pendulum  Governors.-^In  its  simplest  form  the  pendulum 
governor  consists  of  two  balls  suspended  upon  a  vertical  shaft 
as  in  fig.  619.  The  weight  of  the  balls  tends  to  hold  them  down, 
and  centrifugal  force  operating  against   gravity   (or  a  spring) 


366 


GOVERNORS 


tends  to  raise  them  (that  is,  make  them  fly  outward),  as  ex- 
plained in  the  preceding  sections. 

Theoretically,  the  action  of  the  balls  is  independent  of  their  weight 
as  the  centrifugal  force  varies  in  the  same  proportion  as  the  weight  and 
maintains  constant  the  relative  effects,  so  that  at  constant  speed  the  balls 
will  rotate  in  the  same  plane,  whatever  their  weight.  This  is  true  only 
where  the  arms  are  simply  hinged  at  the  top  without  any  other  connections. 


B-i- 

\ 

A 


Fig.  (d19. — Simple  pendulum  governor  actuated  by  centrifugal  force  and  gravity.  In  operation, 
assume  that  at  normal  speed  of  the  engine,  the  balls  revolve  in  the  plane  AA,  then  let  part 
of  the  load  be  thrown  off  and  the  engine  will  speed  up  slightly,  or  enough  to  throw  the  balls 
into  some  higher  plane  as  BB.  This  raises  the  collar  on  the  spindle  from  C,  to  D,  and  by  means 
of  a  lever  attachment  or  equivalent,  control  the  steam  supply  by  throttling  or  variable  cut 
off  according  as  the  governor  is  of  the  throttling  or  cut  off  type. 


In  a  governor  as  constructed  there  are  a  collar,  side  rods,  etc., 
which,  having  no  rotary  motion  tending  to  raise  them  by  cen- 
trifugal force,  act  as  dead  weights  on  the  balls  and  cause  them 
to  revolve  in  a  lower  plane.  However,  if  the  balls  be  made 
heavy  in  comparison  with  the  weight  of  the  arms  and  collar, 
this  effect  becomes  small. 


GOVERNORS 


367 


368  GOVERNORS 


The  expression  for  the  total  centrifugal  force  horizontally  outward  is: 

'  ..C  =  12  W^;2-^gr .    .     (1) 

in  which 

C  =  total  centrifugal  force  in  lbs. ; 
W  =  weight  of  both  balls  in  lbs. ; 

z;=  tangential  velocity  of  balls  in  feet  per  second; 
'    g  =  acceleration  due  to  gravity  =  32.16;  ; 

'  r^radius  of  rotation  of  the  balls,  in  inches. 
In  the  previous  section  was  obtained  the  expression 

Wr  =  Ch (2) 

Substituting  for  C,  its  value  as  in  (1), 

Wr  =  12W  v^h^gr (3) 

from  which 

h=gr^-^12v^ (4) 

Now  the  tangential  velocity  v,  of  the  balls  for  any  rotative  speed  R,  is 

1^  =  2  TT  r  R^  (12X60)  =xrR-T- 360 

and  since  g  =  32. 16,  substituting  in  (4) 

7i  =  32.16r2-M2  (7^rR^360)2  =  35,191.7-^R2         (5) 

Example. — In  an  engine  running  at  200  r.p.m.,  the  governor  is  to  run 
at  half  that  speed  and  have  a  "regulation"  within  4  per  cent. 

Four  per  cent  regulation  means  that  the  maximum  speed  of  the  engine 
is  to  be 

200X1.02=204  r.  p.  m 

and  the  minimum  speed 

200 X. 98  =  196  r.  p.  m. 

Then  the  corresponding  maximum  and  minimum  speeds  of  the  governor 
will  be  half  these  values  or  102  and  .98  r.  p.  m.  respectively.  Substituting 
these  values  in  (4),  for  maximum  speed 

h  =  35,l9l.7^1022  =  3.38  ' 

and  for  minimum  speed 

h  =  35,191.7^  982  =  3.66 

which  means  that  the  balls  must  rise  and  fall  vertically  a  distance  of 

3.66  — 3.38  =  .28  inch 

for  a  total  variation  of  4  per  cent  in  the  speed  of  the  engine,  that  is  for 
4  per  cent  regulation.  The  corresponding  movement  of  the  collar  upon 
the  governor  shaft  will  depend  upon  the  lengths  of  the  different  arms  and 
connecting  levers  and  may  be  determined  graphically. 


GOVERNORS 


sm 


Loaded  Pendulum  Governors. — In  the  example  given  in 
the, preceding  section  it  is  evident  that  there  is  but  little  change 
in  the  height  of  the  governor  for  even  considerable  variation 
in  speed,  and  also  that  for  high  speeds,  the  height  h  of  the 
governor  becomes  so  small  that  the  mechanism  would  be 
difficult  to  construct.  To  overcome  these  defects  the  governor 
may  be  loaded,  that  is,  a  weight  is  placed  on  the  collar  to  assist 
gravity  in  holding  down  the  balls  as  in  fig.  623. 


LOAD 


COLLAR 


Fig.  623. — Diagram  of  loaded  pendulum  governor.     In  this  type  a  weight  (or  equivalent)  is 
placed  on  the  collar,  thus  increasing  the  gravity  effect  in  resisting  the  centrifugal  force. 


The  governor  equation  already  found  may  be  stated  as 
gravity  moment  =  centrifugal  force  moment 
or  in  symbols 

Wr  =  Ch (6) 

Now  if  W,  be  the  combined  weight  of  the  balls,  as  before,  and  W  the 
weight  of  the  load  placed  upon  the  collar  as  in  fig.  623,  then  the  gravity 


370 


GOVERNORS 


moment  is  (W+W)  r,  which  substituted  for  W  in  equation  (6)  gives 

(W+WO  r  =  Ch (7> 

Substituting  in  (7)  the  value  of  C,  as  found  in  (1) 
(W+W)  r  =  12  W  v'^h^gr 
from  which,  solving  for  h 


CO 
UJ 

5  ^ 


o 
o 


v9 
UJ 

X 


(8) 


iO 


12  - 


Fig.  624. — Reasan  for  loading  a  governor.  If  the  height  h,  for  a  simple  pendulum  governor  be 
calculated  for  different  speeds,  it  will  be  found  that  while  the  change  of  height  h,  for  a  change 
of  speed  may  be  comparatively  large  when  the  speed  of  the  governor  is  low,  when  the  speed 
is  increased,  the  change  of  height  for  a  change  of  speed  becomes  so  small  as  to  be  of  no 
practical  value.  Thus  in  the  figure  from,  say  60  to  70  revolutions,  the  difference  in  h,  is 
large,  and  say  from  110  to  120,  it  is  very  small.  Hence  if  a  weight  or  load  be  added  which 
increases  the  gravity  effect,  then  a  large  movement  of  the  sleeve  may  be  obtained  with  a 
high  speed  of  rotation,  and  at  the  same  time  a  much  more  powerful  governor  is  obtained 
than  when  no  central  load  is  used. 


It  will  be  noticed  that  the  second  factor  of  (8)  is  the  same  as  the  value 
ofh,m  equation  (4),  and  reduced  in  (5),  hence  substituting  the  value  given 
in  (5)  in  equation  (8). 

^_W+W'      35,191.7 


w 


R2 


GOVERNORS  371 


from  which  it  appears  that  the  height  h,oi  a  loaded  governor  is  greater  than 
an  unloaded  one  to  the  extent  of  the  factor  (W+W)"^  W. 

Assuming  the  load  upon  the  collar  to  be  1,  then  for  maximum  speed 


/;  =i±^x55|^  =  6x3.38  =20.28 

and  for  minimum  speed 

7^=^x55^^  =  6X3.66  =  21.96 

Then  the  vertical  movement  of  the  collar  will  be  21.96  —  20.28  =  1.68 
in.,  as  compared  with  .28  in  the  example  of  the  unloaded  governor  just  given. 

Ones.     How  is  the  load  proportioned? 

Ans.     It  is  usually  made  much  heavier  than  the  balls. 

Oues.  What  equivalent  is  sometimes  used  in  place  of 
a  weight  on  loaded  governors? 

Ans.     Springs. 

These  are  used  especially  on  throttling  governors  and  are  so  attached 
that  they  oppose  the  centrifugal  force  obtaining  the  same  effect  as  a  weight. 

Owes.  How  may  a  loaded  governor  be  constructed  and 
why? 

Ans.  It  may  have  comparatively  small  rotating  weights, 
because  the  centrifugal  force  increases  as  the  square  of  the 
number  of  revolutions  and  only  directly  as  the  weight  of  the  balls. 

Sensitiveness. — A  governor  is  said  to  be  sensitive  when  a 
small  variation  of  speed  causes  a  considerable  movement  of  the 
regulating  mechanism. 

Theoretically,  loading  a  governor  has  no  effect  on  its  sensi- 
tiveness however  since,  in  practice,  the  friction  of  the  governor 
and  regulating  mechanism  may  be  considerable,  the  sensitiveness 
of  a  loaded  governor  is  actually  much  greater  than  that  of  the 
unloaded  type. 


372 


GOVERNORS 


About  2  per  cent 
variation  of  speed  of 
the  engine  may  be 
considered  as  the 
practical  limit  of  vari- 
ation with  good  gover- 
nors. A  less  percent- 
age than  this  reqmres 
an  abnormally  large 
fly  wheel. 

Figs.  625  to  628 
show  several  types  of 
pendulum  governors 
arranged  in  the  order 
of  their  sensitiveness, 
fig.  625  being  the  least 
sensitive,  and  fig.  628 
the  most  sensitive. 

Stability.— A 

governor  is  said  to  be 
stable  when  it  main- 
tains a  definite  position 
of  equilibrium  at  a 
given  speed. 

When  the  reverse 
conditions  obtain,  it 
is  said  to  be  unstable, 
that  is,  when  at  a 
given  speed  it  assumes 
indifferently  any  po- 
sition throughout  its 
range   of   movement. 


GOVERNORS 


373 


Oues.     What  is  the  condition  for  stability? 

Ans.     For  stability,   the  centrifugal  force  must  increase  more 
rapidly  than  the  radius  of  rotation  of  the  halls. 

Evidently  no  governor  can  maintain  a  constant  speed  since  it  requires 
a  change  of  speed  to  actuate  the  regulating  mechanism.  When  the  balls 
are  in  the  lowest  position  the  regulating  mechanism  gives  the  full  steam 
supply  for  maximum  load  and  when  the  balls  are  highest,  just  enough  to 
run  the  engine  against  its  frictional  load. 


Fig.  629. — Early  form  of  parabolic  governor,  which  operates  isochronously,  that  is,  the  slightest 
variation  of  speed  drives  the  balls  to  the  end  of  their  travel.  This  condition  is  only  obtained 
when  the  balls  in  rising  and  falling  describe  a  portion  of  a  parabola,  for,  in  this  case  the 
height  of  the  cone  of  revolution  is  constant  for  all  positions  of  the  arms,  and  the  balls  are 
in  equilibrium  and  will  remain  in  any  position,  so  long  as  the  speed  remains  unchanged.  The 
above  construction  which  is  said  to  be  the  earliest  form  of  parabolic  governor  known  in 
England  was  introduced  in  1851.  The  balls  were  suspended  by  links  to  rollers,  which  traveled 
upon  arms  branching  from  a  vertical  spindle,  so  formed  that  the  centers  of  the  rollers  traveled 
in  a  parabolic  curve.  An  early  governor  of  this  type  applied  to  a  compound  engine  was 
rendered  useless  by  its  excessive  sensitiveness,  continually  operating  the  throttle  valve. 
The  difficulty  was  overcome  by  applying  an  air  dash  pot. 

If  the  boiler  pressure  or  the  load  be  changed,  a  certain  amount  of  dis- 
placement of  the  balls  is  necessary  to  vary  the  steam  supply,  and  this 
displacement  can  only  be  obtained  by  a  change  in  speed,  hence  the  term 
constant  speed  is  erroneously  used  as  applied  to  engines  where  speed  is 
controlled  by  a  governor. 


374 


GOVERNORS 


Isochronism. — A  governor  is  said  to  be  isochronous  when 
it  is  in  equilibrium  at  only  one  speed. 

If,  when  the  balls  are  displaced,  the  centrifugal  force  changes  pro- 
portionately to  the  radius  of  rotation  of  the  balls,  the  speed  is  constant, 
that  is,  the  equilibrium  of  the  governor  is  neutral,  allowing  it  to  revolve  in 
equilibrium  at  only  one  speed. 

The  slightest  variation  in  speed  drives  the  balls  to  the  end  of  the  travel. 
Such  a  governor  is  said  to  be  isochronous,  and  its  sensitiveness  is  theo- 
retically infinitely  great. 


APPROXIMATE. 
PARABOLA 


Fig.  630.— Diagram  of  crossed  arm  pendulum  governor,  the  approximate  equivalent  of  the 
parabolic  type.  By  producing  the  two  extreme  positions  of  an  arm  BA  and  B'A',  until 
they  intersect  at  P,  and  using  this  as  a  point  of  suspension.  The  curve  described  by  the  balls 
during  their  travel  will  approximate  a  parabola  and  the  action  of  the  governor  will  be 
approximately  isochronous. 

Oues.     What  type  of  governor  is  isochronous? 

Ans.     The  parabolic  governor. 

Hunting. — An  isochronous  governor  cannot  be  used  success- 
fully on  an  engine  without  being  modified  so  as  to  obtain  a  small 
margin  of  stability  to  prevent  violent  changes  in  the  steam 


GOVERNORS  375 


supply,  especially  if  there  be  much  f fictional  resistance  to  be 
overcome  by  the  governor,  or  where  the  engine  responds  slowly 
to  the  influence  of  the  governor.  When  a  change  of  speed  occurs, 
however  quickly  the  governor  acts,  the  engine's  response  is 
more  or  less  delayed. 

Jf  the  regulation  be  by  throttling,  the  steam  chest  forms  a  reservoir  to 
draw  upon,  and  if  by  variable  cut  off,  the  opportunity  is  lost  if  cut  off 
has  already  occurred,  and  control  cannot  begin  until  the  next  stroke.  A 
sudden  decrease  of  load  is  accompanied  by  such  increase  in  speed  as  to 
cause  abnormal  governor  action  giving  too  little  steam  for  the  reduced 
load.  Causing  a  decrease  of  speed  accompanied  by  excessive  increase  in 
the  steam  supply.  The  governor  thus  oscillates  in  its  endeavor  to  find  a 
position  of  equilibrium  and  such  action  brought  on  by  over-sensitiveness 
is  called  hunting. 

Oues.  What  form  of  governor  is  approximately  the 
equivalent  of  a  parabolic  governor? 

Ans.     The  pendulum  governor  with  crossed  arms  as  in  fig.  630. 

Oues.     How  is  the  stability  of  this  governor  varied  ? 

Ans.  Reducing  the  distance  PA,  increases  the  stability; 
increasing  P  A,  gives  the  reverse  effect.  If  the  point  P,  be  too 
far  from  the  spindle,  the  height  of  the  cone  may  increase  as  the 
balls  rise  and  cause  unsatisfactory  operation. 

Inertia  Governors. — The  term  inertia  may  be  defined  as 
that  property  of  a  body  by  virtue  of  which  it  tends  to  continue  in  a 
state  of  rest  or  motion  in  which  it  may  be  placed  until  acted  upon 
by  some  force.  This  forms  the  working  principle  of  inertia 
governors,  and  in  general  an  inertia  governor  may  be  said  to 
consist  of  a  heavy  body  pivoted  at  its  center  of  gravity  and 
connected  at  a  proper  point  to  the  regulating  mechanism. 

In  operation,  the  heavy  body  revolving  in  step  with  the  fly  wheel  tends 
^K^o  revolve  at  constant  speed.    Any  change  of  speed  of  the  fly  wheel  due  to 


376 


GOVERNORS 


c3  O  Jj  be  O^T" 

w      g^o.S  gS.rt  o  ^^ 


GOVERNORS  377 


variable  load  produces  a  change  in  the  position  of  the  heavy  body  with 
respect  to  the  wheel,  thus  moving  the  regulating  mechanism. 

The  so  called  inertia  governors  found  on  many  are,  strictly  speaking, 
combined  centrifugal  and  inertia  governors,  as  their  action  depends  on 
both  forces.  According  to  constructing,  one  force  may  be  made  to  either 
oppose  or  assist  the  other. 

In  fig.  631  a  governor  disc  is  pivoted  to  the  fly  wheel  at  P,  as  shown.  If 
the  wheel  rotate  in  the  direction  of  the  arrow,  an  increase  in  speed  will 
cause  the  disc  to  move  outward  from  the  center  C,  by  centrifugal  force, 
but  if  the  governor  disc  be  pivoted  at  the  center  of  the  shaft  as  in  fig.  632, 
then  the  centrifugal  force  acting  radially  with  respect  to  the  pivot  P,  will 
have  no  effect  on  the  disc  since  the  position  of  the  pivot  P,  coincides  with 
the  center  C,  of  the  fly  wheel. 

•  If  in  fig.  632  the  speed  of  the  fly  wheel  increase  or  decrease,  the  disc, 
(tending  to  rotate  at  constant  speed)  will  respectively  lag  behind  or  advance 
beyond  the  position  shown  in  the  figure,  that  is,  it  will  move  with  respect 
to  the  fly  wheel  in  the  direction  of  I,  or  I',  respectively,  inertia  in  this  case 
alone  being  the  controlling  force,  the  resisting  force  being  the  tension  of 
the  spring. 

In  fig.  632  the  force  due  to  inertia  is  a  maximum.  This  force  may  be 
made  to  assist  or  oppose  the  centrifugal  force  according  to  the  location  of 
the  pivot  P.  Thus  in  fig.  633,  if  the  fly  wheel  be  rotating  in  the  direction 
of  the  arrow,  both  forces  act  together  and  make  the  governor  rapid  in  its 
movement,  while  in  fig.  634,  the  forces  oppose  each  other  and  tend  to  make 
the  governor  sluggish. 

Another  form  is  shown  in  fig.  635,  in  which  the  centrifugal  force  is 
neutralized,  the  controlling  force  being  due  to  inertia  alone.  In  the  figure 
two  discs  A  and  B,  connected  by  an  arm  are  pivoted  at  the  center  of  gravity 
P,  at  a  distance  C  P,  from  the  center  C,  of  the  fly  wheel. 

In  operation  when  the  fly  wheel  revolves  disc  A,  is  acted  upon  by  a 
centrifugal  force  F,  and  B,  by  an  equal  centrifugal  force  F'.  These  forces 
acting  on  opposite  sides  of  the  pivot  P,  and  at  equal  distances  neutralize 
each  other. 

Now  if  the  fly  wheel  revolve  in  the  direction  of  the  arrow,  and  its  speed 
be  decreased,  the  inertia  of  the  discs  (represented  by  the  forces  I'  I')  will 
cause  them  to  revolve  around  P,  to  some  position  as  A'  B'.  Clearly  if  the 
speed  increase  the  reverse  condition  will  obtain,  that  is,  the  discs  will 
revolve  around  P,  to  some  position  as  A"  B",  under  the  influence  of  the 
inertia  forces  V  V, 


Spring  Governors. — The  use  of  springs  for  the  controlling 
force  or  to  assist  gravity  is  quite  common.  When  springs  are 
used  the  ball  aims  may  be  arranged  to  travel  across  a  vertical 


378 


GOVERNORS 


5,  K   <U   <U   <U  '^   -^ 


A 

V 

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c 

e. 

^ 

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Ul 

IS 

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J 

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1 

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i/     * 

5         wpq  ^  d  ^  o 
l.i^.brrt  +^       M  <u  a> 


GOVERNORS  379 


axis,  or  the  governor  may  be  operated  in  a  horizontal  position 
and  gravity  practically  eliminated. 

Spring  governors  can  be  made  practically  isochronous  if  desired,  by  so 
adjusting  the  spring  that  the  initial  compression  in  the  spring  bears  the 
same  ratio  to  the  total  compression  that  the  minimum  radius  of  the  balls 
bears  to  the  maximum  radius.  .a- 

In  practice,  stability  is  provided  by  making  the  spring  a  little  stronger 
than  the  above  adjustment. 

Fig.  692  illustrates  the  operation  of  a  spring  governor.  As  shown,  the 
balls  are  attached  to  bell  crank  arms,  pivoted  at  P  and  P',  to  a  frame, 
which  revolves  around  the  central  upright  shaft.  The  travel  of  the  balls  is 
transmitted  by  the  bell  cranks  to  the  collar  at  A  A'.  An  adjustable  spring 
presses  against  the  collar  and  acts  as  a  substitute  for  gravity. 

In  operation  as  the  speed  increases  the  centrifugal  force  increases  and 
the  balls  move  outward.  The  compression  on  the  spring  increases  similarly, 
and  by  suitably  adjusting  the  initial  pressure  on  the  spring,  the  governor 
may  be  made  nearly  isochronous,  as  before  mentioned,  and  rendered  very 
sensitive,  which  is  a  ch^,racteristic  of  this  class  of  governor. 

The  Regulating  Mechanism. — This  term  is  applied  to  the 
gearing  or  * 'transmission"  which  transmits  the  movement  of  the 
governor  to  the  control  device. 

Figs.  636  to  QA2.— Continued. 

(fig.  637),  by  having  more  tension  on  the  eccentric  arm  spring  C^,  than  is  maintained  on 
the  spring  attached  to  the  other  arm  C  By  this  arrangement  any  amount  of  friction 
necessary  for  stability  is  obtained.  The  eccentric  D,  is  fastened  to  one  arm  A',  in  its  proper 
relation  to  the  suspension  and  crank  pin  so  that  the  swinging  of  the  arms  move  the  eccentric 
across  the  shaft,  changing  its  throw,  producing  the  desired  effect  of  changing  the  cut  off 
of  the  valve.  The  sliding  block,  C-^,  to  which  the  arm  ends  of  the  springs  are  attached  is 
used  to  increase  the  range  of  the  springs.  In  adjusting,  by  moving  the  sliding  block  along 
the  grooves  C^,  the  points  of  .suspension  are  changed.  By  changing  the  points  of  suspension 
any  desired  effect  upon  the  action  of  the  governor  is  obtained.  The  inertia  arms  are  pur- 
posely made  heavy  so  as  to  balance  the  reciprocating  parts  of  the  valve  motion. 


NOTE. — Directions  for  Riblet  combined  centrifugal  and  inertia  governor.  1.  When 
springs  are  placed  in  the  governor,  the  suspension  points  E,  of  the  sliding  block  must  be  about 
half  way  between  their  minimum  and  maximum  positions.  2.  The  free  arm  spring  C^,  must 
be  tightened  just  enough  to  hold  it  in  place.  3.  The  eccentric  arm  spring  CS  must  be  tightened 
so  that  it  is  pulled  out  about  ^",  or  just  enough  to  stop  the  rattle  of  the  governor.  4.  Start 
the  engine.  5.  If  the  engine  run  too  fast,  put  shot  in  cavity  B^  and  the  same  amount  in  B^. 
6.  If  the  engine  run  too  slow,  put  shot  in  cavities  B2  and  B*.  7.  Until  the  point  is  reached  where 
the  required  speed  is  obtained  pay  no  attention  to  regulation.  When  the  speed  is  obtained 
apply  load  to  the  engine.  8.  If  the  engine  run  slower  as  the  load  is  applied,  move  the  springs 
by  means  of  the  sliding  block  toward  their  maximum  position  in  direction  of  arm,  fig.  642  of 
their  points  of  suspension  E;  continue  this  movement  until  the  desired  regulation  is  reached. 
9.  If  engine  run  faster  as  the  load  is  applied,  reverse  the  procedure  given  in  8.  10.  Be  sure 
the  governor  does  not  stick  or  bind  and  that  the  suspension  pins  are  well  lubricated  with  good 
grease. 


380 


GOVERNORS 


kO  D, 


^25  S 


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ft^  o^  o'-^  5  ^  .-a, 

-oj  .-.^  §§^  ft^.S-^^ 
-^  .«^  '^  .;r<N^  W.2  ^ 

^:5i-H  w  ^  '-'(N  ..'"  cjj 


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*"  _ri  ><  v-' "  5  o  ^  S  -r  - 


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ToQ^  '^^<  a>''^  «> 


S§.s 


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^  o  o 


GOVERNORS 


381 


According   to   the  nature   of  the  regulations   governors   are 
classed  as 

1.  Throttling; 

2.  Cut  off. 

The  throttle  valve  as  introduced  by  Watt  was  what  is  now  known  as  a 
butterfly  valve,  and  consisted  of  a  (^isc  turning  on  a  transverse  axis  across 
the  center  of  the  steam  pipe.    It  is  now  usually  a  globe,  gate,  or  piston  valve. 


Fig.  692. — Elementary  diagram  showing  working  principle  of  spring  governors. 

When  regulation  is  effected  by  varying  the  cut  off,  an  expansion  valve 
or  the  slide  valve  or  piston  type  is  used,  the  governor  generally  acts  by 
changing  the  travel  of  the  valve.  In  some  forms  of  automatic  expansion 
gear,  the  lap  of  the  valve  is  altered ;  in  others,  the  governor  acts  by  rotating 
the  expansion  valve  eccentric  on  the  shaft  and  so  changing  the  angular 
advance.    These  matters  are  fully  explained  in  the  chapters  on  valve  gears. 


Throttling  Governors. — If  this  type  of  governor  had  never 
been  invented,  no  doubt  some  of  the  world's  natural  resources 


382 


GOVERNORS 


Fig.  695.— Pickering  "ball 
speed  ranger,"  permits 
increasing  speed  of  engine 
50  to  7o  per  cent  from 
normal  by  turning  the 
small  hand  wheel,  which 
can  be  done_  while  the 
engine  is  running. 


Fig.  693. — Pickering  class  A  throt- 
tling governor  fitted  with  auto- 
matic safety  stop,  speed  regulator 
and  sawyer's  lever. 


Fig.  694. — Pickering  class  B 
throttling  governor  fitted 
with  speed  regulator  and 
sawyer's  lever. 


Fig.  696. — Sinker-Davis  "Hoosier"  throttling  governor  with  wide  range  speed  regulator 
permitting  variation  of  150  revolutions.  Adjustment:  Adjust  coil  springs  only  to  the  point 
where  the  valve  works  freely  and  easily.  Only  sufficient  tension  is  required  to  balance  the 
valve  against  the  steam  resistance.  The  coil  springs  are  not  for  speed  regulation.  To  change 
the  speed:  Loosen  the  lock  nuts  at  the  top  of  the  governor  above  the  traveling  head,  and 
if  engine  speed  is  to  be  increased,  run  the  nuts  down  until  the  speed  increases  to  the  revolutions 
wanted,  then  lock  them.  If  the  speed  is  to  be  decreased,  run  the  nuts  up  until  the  speed 
decreases  to  the  revolutions  wanted,  then  lock  them.  The  regular  speed  of  the  governor  is 
stamped  on  the  traveling  head,  and  a  variation  of  speed  not  exceeding  75  revolutions,  slower 
or  faster,  can  be  obtained  by  changing  the  nuts  as  explained  above.  If  more  variation  be 
required,  change  the  pulley  on  the  main  shaft  of  engine  to  give  required  speed  on  engine  and 
on  governor.  The  cam  or  automatic  stop  is  adjustable  for  either  right  or  left  hand  engines. 
The  governor  should  be  well  oiled  before  starting,  but  can  be  oiled  while  in  motion  by  oiling 
above  the  traveling  head  only;  the  oil  will  work  down  through  the  governor,  and  it  is  not 
necessary  to  oil  at  any  other  point.  In  packing  the  stuffing  box,  be  sure  to  see  that  the  valve 
stem  works  freely  and  without  tension  on  the  coil  springs. 


GOVERNORS 


383 


would  be  better  preserved  and  the  price  of  fuel  not  so  high. 
However,  for  some  services  where  waste  material  is  to  be  dis- 
posed of,  and  can  be  used  as  fuel,  a  throttling  governor  may  be 
employed.  This  type  of  governor  may  be  defined  as  an  auto- 
matic throttle  valve  which  governs  by  altering  the  pressure  at 
which  steam  is  admitted  to  the  cylinder;    that  is,   the  throttle 


Figs.  697  and  698. — ^Waters  spring  throttling  governor.  Fig.  697  shows  class  A,  fitted  with 
automatic  safety  stop  in  which  a  spring  throws  the  shaft  out  of  gear  when  the  governor  belt 
breaks.  In  erecting,  be  sure  and  have  the  end  cap  on  the  bracket  stand  with  the  head  of 
set  screw  pointing  direct  to  the  pulley  on  engine  shaft.  In  operation,  if  the  governor  belt 
break,  the  spring  throws  the  shaft  out  of  gear,  the  top  drops  and  closes  the  valve.  To  start 
again,  raise  the  top  part,  push  the  gears  together  and  hold  it  in  position  while  putting  on 
the  belt.    Fig.  698  shows  governor  fitted  with  sawyer's  lever. 


valve  is  opened  or  closed  inversely  with  changes  in  load,  thus 
causing  more  or  less  drop  in  pressure  so  that  the  resulting  mean 
effective  pressure  in  the  cylinder  will  vary  with  the  load  and 
maintain  a  steady  speed. 


384 


GOVERNORS 


Fig.  700.-;—Gardner  class  B  throttling  governor 
fitted  with  speed  regulator  and  Sawyer's  lever. 
Class  B  combines  both  the  spring  and  gravity 
actions,  adapted  for  all  styles  of  slow  and  medium- 
speed  stationary  engines.  In  operation  the 
centrifugal  force  of  the  balls  operates  against  the 
resistance  of  a  coiled  steel  spring  enclosed  within 
a  case  and  pivoted  on  the  speed  lever;  by  means 
of  a  screw  the  amount  of  compression  on  the 
spring  can  be  changed  so  as  to  give  a  wide  range 
of  speed.  A  continuation  of  the  speed  lever 
makes ^  a  convenient  sawyer's  hand  lever.  By 
attaching  a  cord  to  this  lever  the  valve  of  the 
governor  can  be  controlled  at  a  reasonable  dis- 
tance from  the  governor.  Sizes  from  %  inch  to 
134  inches,  inclusive,  have  swivel  frames  which 
can  be  set  at  any  desired  angle  in  relation  to  valve 
chambers.  The  valves  and  seats  of  this  style  are 
the  same  as  used  on  the  Standard  Class  "A" 
governor. 


Fig.  699. — Gardner  class  A  throt- 
tling governor  fitted  with  auto- 
matic safety  stop  and  speed 
regulator,  sizes  13^  to  16  inches 
inclusive.  Class  A  type  is  of 
the  gravity  action  and  is  espe- 
cially adapted  for  the  larger 
types  of  stationary  engines.  In 
operation  the  centrifugal  force 
of  the  balls  is  opposed  by  the 
resistance  of  a  weighted  lever 
and  the  speed  is  varied  by  the ' 
position  of  the  weight  on  the 
lever.  _  The  automatic  safety 
stop  is  accomplished  by  per- 
mitting a  slight  oscillation  of 
the  shaft  bearing,  which  is 
supported  between  centers  and 
held  in  position  by  the  pull  of 
the  belt;  a  projection  at  the 
lower  part  of  the  shaft  bearing 
supports  the  fulcrum  of  the 
speed  lever.  If  the  belt  break 
or  slip  off  the  pulley,  the  support 
of  the  fulcrum  is  forced  back, 
allowing  the  fulcrum  to  drop, 
closing  the  valve.  The  valve 
chamber  is  fitted  with  valve 
seats  made  of  a  composition. 
The  valve  is  of  the  same  ma- 
terial. This  style  is  made  for 
both  horizontal  and  vertical 
engines. 
^^..^—^■■^--~. 


GOVERNORS 


385 


Fig.  702  shows  the  effect  of  a  throttling  governor  upon  the^ 
indicator  diagram. 

V/hen  working  under  full  load,  the  diagram  has  the  form  shown  by  the 
full  line,  but  when  the  load  drops,  and  the  engine  speeds  up  slightly,  the 
governor  acts,  partially  closes  the  throttle  valve,  and  the  pressure  is  reduced 


Fig,  701, — Gardner  speed  and  pressure  regulator  fitted  with  automatic  stop  for  steam  actuated 
compressors.  This  regulator  consists  of  a  class  A  governor  fitted  with  a  brass  cylinder  con- 
taining a  piston  upon  which  the  air  pressure  is  exerted.  The  brass  cylinder  is  connected  by 
a  pipe  with  the  air  receiver  set  about  25  feet  distant  from  the  regulator,  so  that  the  latter 
may  always  be  under  the  direct  influence  of  the  air  pressure  within  the  receiver.  The  air ' 
pressure  to  be  maintained  is  regulated  by  the  position  of  the  weight  on  the  lever.  When 
this  pressure  has  been  reached  it  is  exerted  on  the  brass  piston,  pushing  it  upward  and  closing 
the  governing  valve,  or  keeping  it  open  just  wide  enough  to  maintain  a  constant  air  pressure. 
On  duplex  machines,  when  the  desired  air  pressure  has  been  attained,  the  regulator  will 
bring  compressor  to  a  dead  stop,  starting  it  up  automatically  when  air  pressure  falls  below 
the  required  amount.  On  single  compressors  it  is  not  desirable  to  bring  the  compressor  to 
a  dead  stop,  and  there  is  an  adjustable  device  on  the  regulator  which,  when  set  for  certain 
pressure,  will  allow  the  compressor  to  just  turn  over  when  that  pressure  has  been  attained. 
The  standard  or  ball  governor  acts  merely  as  a  speed  controller;  it  has  no  throttling  action 
on  the  steam  until  the  limit  of  speed  has  been  reached.  By  the  use  of  properly  proportioned 
pulleys  on  the  governor  and  compressor,  provision  can  be  made  for  the  proper  speed  limit. 
The  ball  governor  keeps  the  compressor  from  exceeding  this  limit,  and  it  thus  serves  to  pre- 
vent the  engine  running  away  in  case  of  sudden  loss  of  air  pressure  from  any  cause. 


386 


GOVERNORS 


BOaeR  PRESSURE 
A 


CONSTANT  CUT  OFF 


\}\.L  THROTTLE  ADMlSSfON 
(heavy- load) 


PARTLY  CLOSED  THROTTLE  ADMISSION 
(light  LOADJ 


Pig.  702. — Indicator  diagram  showing  action  of  throttling  governor. 


/    PULLEY  BE.LTE:D  TO 

PULLEY  OKI  ENGINE  SHAFT 


STEAM  FROM 
BOILER 


SUPPLY  TO  ENGINE 


Fig.  703. — S  e  c  t  i  o  n  a  1 
view    of    throttUng 
governor    showing 
general    construction. 
The    names    of     the 
parts  are:  1,  standard; 
2,  governor  shaft;  3, 
governor  balls;  4,  arms;  5,  stem  swivel; 
6,  pivots;    7,  gears;    8,  pulley;    9,  oil 
holes;  10,  stem;  11,  bonnet;   12,  stuffing 
box;  13,  gland;  14,  gland  box;  15,  valve 
discs;    16,  valve  seats;    17,  stem  guard; 
18,   throttle  valve    flange;    19,   valve 
chest  flange. 


GOVERNORS 


387 


by  wire  drawing  so  that  the  admission  and  expansion  lines  take  the  posi- 
tions shown  by  the  broken  lines  in  the  illustration.  The  resulting  drop 
in  pressure  is  always  proportional  to  the  reduction  in  load,  so  that  the 
speed  remains  constant,  or  practically  constant  within  certain  limits, 
whatever  the  load  upon  the  engine. 

The  general  construction  of  a  throttling  governor  is  shown 
in  fig.  703. 


Fig.  704.— -Gardner  spring  throttling  governor  with  speed  regulator,  sawyer's  lever,  and 
automatic  safety  stop.  This  governor  is  recommended  for  traction  and  high  speed  stationary 
engines.  It  is  very  quick  and  sensitive  in  action,  and  is  therefore  capable  of  responding 
promptly  to  the  various  changes  in  load.  The  balls  are  rigidly  connected  to  steel  springs, 
the  lower  ends  of  the  springs  being  secured  to  a  revolving  sleeve  which  receives  its  rotation 
through  mitre  gears;  links  connect  the  balls  to  an  upper  revolving  sleeve,  which  is  free  to 
move  perpendicularly.  The  balls  at  the  free  ends  of  the  springs^  funiish  the  centripetal 
force,  and  the  springs  are  the  main  centripetal  agents.  No  gravity  is  employed.  Sizes, 
3^  to  7  inches. 


The  valve  15  is  of  the  balanced  or  double  seat  poppet  type. 

A  different  type  of  valve  is  shown  in  fig.  705  which  is  a  sectional  view 
of  the  regulating  mechanism  of  the  Waters  throttling  governor. 


388 


GOVERNORS 


Cut  Off  Governors. — In  this  method  of  regulation,  which 
is  always  used  where  any  regard  is  had  for  economy,  steam  is 
admitted  with  full  throttle  opening  and  the  mean  effective  pressure 
controlled  to  suit  the  load  by  varying  the  point  of  cut  off. 


PISTON 
VALVE 


VALVE 
SEAT 


STEAM 

FROM  BOILER 

Fig.  705. — Regulating 
mechanism  of  the 
Waters  throttling 
governor.  In  con- 
struction, the  valve 
is  of  the  triple  ported 
piston  type,  both 
valve  and  seat  being 
made  of  composition 
metal.  The  arrows 
show  the  paths  of  the 
steam.  Ample  ad- 
SUPPLY  TO  ENGINE  mission  area  is  secured 

by  the  three  ports.  The  four  valve  seats  are  all  in  one  casting,  which  fits  the  iron  body  at  the 
ends  only,  providing  for  expansion  and  contraction.  The  valve  being  of  the  piston  type  is 
balanced  and  the  triple  ports  give  the  required  admission  with  a  correspondingly  small  travel. 


BOluER    PRESSURE 


-  EARLY   CUT  OFF  -  UGHT  UQAO 
-LATE  CUT  OFF    HEAVY  LOAD 


Fig.  706. — Indicator  diagram  illustrating  regulation  by  variable  cut  off. 


GOVERNORS 


389 


Fig.  706  shows  the  resulting  changes  upon  the  indicator  dia- 
gram. Here  the  initial  pressure  remains  the  same,  but  the  area 
of  the  card,  and  consequently  the  amount  of  work,  is  reduced 
by  shortening  the  cut  off.  The  original  and  final  areas  of  the 
diagrams  are  the  same  in  each  case,  and  the  reduction  in  work 
per  stroke  is  shown  by  the  shaded  area. 


ROD 


Pig.  707. — Hartwell  spring  ball  governor  with  variable  cut  off  regulating  mechanism.  In 
operation,  as  the  speed  increases,  the  governor  raises  the  position  of  lever  A,  and  the  travel 
of  the  valve  is  reduced.  This  governor  is  capable  of  very  close  regulation,  and  when  the  speed 
exceeds  a  given  number  of  revolutions,  the  steam  supply  may  be  entirely  cut  off. 


In  this  class  of  governor,  variable  cut  off  is  effected  in  several 
ways,  as  by 

1.  Variable  travel  of  the  valve; 

2.  Variable  angular  advance-; 

3.  Combined  variable  travel  and  variable  angular  advance. 

Fig.  707  shows  a  spring  ball  governor  with  regulating  mechanism  for 


390 


GOVERNORS 


varying  the  cut  off  by 
the  first  method.  As 
shown,  the  regulating 
mechanism  regulates 
the  travel  of  a  riding 
cut  off  valve  by  the 
movement  of  the  lever 
A,  in  the  slotted  link  B. 

Regulation.— The 

term  regulation  means 
speed  variation, 
usually  expressed  as  a 
percentage  of  the 
normal  speed  of  an 
engine,  running  under 
control  of  a  governor. 

Fig.  708. — Nordberg  automatic 
cut  off  governor.  This  device 
is  a  combination  of  trip  cut 
off  gear  and  a  governor  for  con- 
trolling the  same,  designed  to 
be  attached  to  the  steam  pipe 
of  slide  valve,  rocking  valve 
and  similar  engines  to  regulate 
the  speed  of  the  engine.  The 
steam  is  admitted  at  full  boiler 
pressure;  is  cut  off  at  a  point 
corresponding  to  the  demand 
for  power,  and  expanded.  In 
construction,  the  governor 
consists  of  a  double  beat 
poppet  valve,  operated  by  a 
double  trip  mechanism.  A 
sensitive  regulator  sets  the 
point  of  cut  off,  according  to 
the  demand  for  steam.  The 
range  of  cut  off  obtainable  is 
from  0  to  M  or  3^  of  stroke. 
An  air  dash  pot  causes  the 
valve  to  drop  gently  on  the 
seat.  All  contact  edges  about 
the  trip  gear  are  made  in 
shape  of  removable  hardened 
plates,  of  best  English  steel. 
These  plates  are  reversible, 
and  all  eight  edges  can  be 
used  as  contact  edges.  The  cut  off  gear  is  operated  by  an  independent  eccentric  furnished  with 
the  machine;  the  regulator  is  driven  by  a  belt.  A  safety  stop  is  provided  which  will  stop  the 
engine  in  case  of  any  accident  to  the  governor  belt,  or  if  the  regulator  should  stick,  i He  saiety 
stop  will  keep  a  uniform  tension  on  the  governor  belt.    Speed  of  governor  up  to  2UU  r.p.m. 


GOVERNORS 


391 


The  conditions  of  load  vary  widely  in  different  classes  of  work.  In  the 
case  of  factory  or  mill  engines,  the  load  is  practically  constant,  while  wit!?, 
those  employed  for  electric  railway  work,  the  load  changes  constantly  as 
the  various  cars  along  the  line  are  started  and  stopped.  In  the  case  of 
rolling  mill  engines,  the  conditions  are  even  worse,  for  here  the  engine  may 
be  running  light,  with  no  load  except  its  own  friction,  when  suddenly  the 
rolls  are  started  and  the  maximum  load  will  be  thrown  on  at  once. 

With  any  governor  of  whatever  type,  there  must  be  a  certain  variation 
in  the  speed  of  the  engine  to  operate  it.  In  most  well  designed  engines  the 
speed  will  not  vary  more  than  two  per  cent  above  or  below  the  mean  speed, 
and  in  many  cases  even  closer  regulation  is  obtainable. 


Figs.  709  and  710. — McEwen  right  hand  engine  governor;  fig.  363  run  over  setting;  fig.  364, 
run  under  setting.  The  wrist  pin  is  shown  at  2;  there  is  another  hole  in  the  arm  directly 
below.  3  is  a  dash  pot,  and  as  centrifugal  force  interferes  with  its  free  operation  at  high 
speeds  the  weight  4,  is  provided  to  counterbalance  it  and  prevent  undue  friction.  The  governor 
arm  is  pivoted  at  5  and  rubber  buffers  are  provided  at  6  and  7,  the  ends  of  travel.  Fig.  364 
shows  gear  reversed.    The  wrist  pin  is  in  the  other  hole  provided  for  it 


A  regulation  within  4  per  cent  means  that  if  the  normal  speed  of  the 
engine  is  100  r.p.m.  at  its  rated  capacity,  it  should  not  rise  above  102 
r.p.m.  when  all  the  load  is  thrown  off,  nor  drop  below  98  r.p.nr.  when  the 
maximum  load  for  which  it  is  designed  is  thrown  on. 

Oues.    What  is  close  regulation? 

Ans.     Small  speed  variation. 

Owes.     What  is  the  usual  regulation  in  practice? 

Ans.     From  2  to  4  per  cent. 


392 


GOVERNORS 


Shaft  Governors. — This  type  of  governor  is  used  chiefly  in 
that  large  class  of  engines  popularly  known  as  automatic  cut  off 
engines.  Because  of  the  high  rotative  speed,  a  powerful  and 
sensitive  governor  can  be  provided  without  undue  weight  or 
vibration. 

Shaft  governors  may  be  classified: 

1.  With  respect  to  the  controlling  force  or  forces,  as 

a.  Centrifugal; 

b.  Inertia; 


Figs.  711  and  712. — Rites  governor  as  applied  to  Watertown  engine.    Fig.  365,  governor  in 
forward  motion;  fig.  366  governor  reversed. 

c.  Combined  centrifugal  and  inertia; 

d.  Combined  inertia,  and  neutralized  centrifugal. 

2.  With  respect  to  the  regulating  mechanism,  as 

1.  Variable  throw; 

2.  Variable  angular  advance; 

3.  Combined  variable  throw  and  variable  angular  advance. 


Many  of  the  so  called  inertia  governors  are,  in  fact,  of  the 


GOVERNORS 


393 


Figs.  713  and  714. — Harrishurg  governor  in  forward  and  reversed  motion.  The  eccentric  is 
pivoted  at  2,  and  swings  across  the  shaft  3,  by  action  of  the  weights  4  and  5,  which  are  pivoted 
at  6  and  7,  respectively.  After  reversing  governor  as  in  fig.  714,  if  sluggish,  move  the  ends' 
of  the  spring  toward  the  rim  of  wheel;  if  super-sensitive,  move  them  toward  the  center. 


Figs.  715  and  716. — Fitchhurg  governor  in  forward  and  reverse  motion.  When  in  the  position 
shown  the  governor  is  at  rest,  and  the  springs  draw  the  heavy  weights  2  and  3,  inward,  thus 
raising  the  eccentric  to  its  maximum  eccentricity.  In  operation^  centrifugal  force  throws 
the  weights  2  and  3,  outward  against  the  force  exerted  by  the  springs,  reducing  the  eccen- 
tricity until  equilibrium  between  cut  off  and  load  is  established.  The  auxiliary  weight  4, 
operates  with  the  main  weight  2,  as  it  is  pivoted  at  6,  but  the  other  auxiliary  weight  5, 
operates  against  the  main  weight  3,  as  it  is  pivoted  at  7,  hence  4  and  5,  balance  each  other, 
but  taken  together  they  resist  changes  in  speed,  therefore  the  result  is  a  very  steady  speed 
under  variable  load.  If  in  fig.  715,  link  8,  be  disconnected  from  pin  9,  and  connected  at  10, 
the  eccentric  will  be  moved  in  the  opposite  direction  by  centrifugal  force.  By  disconnecting 
link  11,  from  12,  and  connecting  it  at  13,  it  also  reverses  motion  because  it  is  pivoted  at  7, 
these  changes  reversing  the  governor. 


394 


GOVERNORS 


Figs.  717  and  718. — Shaft  governors  illustrating  principles.     Fig.  717,  centrifugal  control, 
variable  throw  regulation;   fig.  718,  inertia  control,  variable  angular  aidvance  regulation. 


Figs.  719  and  720. — Shaft  governors  illustrating  principles.  Fig.  719,  combined  centrffugal 
and  inertia  control  (forces  acting  together),  combined  variable  throw  and  variable  angular 
advance  regulation;  fig.  720,  combmed  centrifugal  and  inertia  control  (forces  acting  in 
opposition),  combined  variable  throw  and  variable  angular  advance  regulation. 


GOVERNORS 


395 


combined  centrifugal  and  inertia  class,  these  forces  acting  either 
in  unison  or  in  opposition  according  to  construction. 

The  principles  relating  to  the  controlling  forces  have  been  explained 
under  inertia  governors,  and  the  methods  of  varying  the  cut  off  by  altering 
the  travel  or  angular  advance,  have  been  treated  at  length  in  chapter  6 
on  variable  cut  off. 

Figs.  717  to  720  show  four  types  of  shaft  governor  illustrating  the  con- 
trolling forces  and  regulating- mechanism  as  classified. 

In  fig.  717  the  action  depends  on  centrifugal  force  alone.  Inertia  acts 
along  the  axis  through  the  pivots  P  P',  and  therefore  does  not  tend  to  rotate 


Figs.  721  and  722. — Shaft  governors  illustrating  principles.  Fig.  721,  inertia  control,  variable 
throw  and  variable  angular  advance  regulation;  fig.  722,  combined  inertia  and  neutralized 
centrifugal  control,  variable  travel  and  variable  angular  advance  regulation. 


the  ball  around  the  pivot.    The  regulating  mechanism  changes  the  cut  off 
by  variable  throw. 

The  governor  illustrated  in  fig.  718,  controls  the  engine  speed  by  inertia 
alone,  the  two  forces  acting  together;  regulation  being  by  variable  angular 
advance. 

Figs.  721  and  722  show  a  regulating  mechanism  with  swinging  eccentric 
which  regulates  by  combined  variable  angular  advance  and  variable  throw. 
The  control  is  by  combined  centrifugal  force  and  inertia,  these  forces 
acting  together  in  fig.  721,  and  in  opposition  in  fig.  722. 


396 


GOVERNORS 


Fig.  721  shows  a  control  by  inertia  alone,  the  regulation  being  by  variable 
angular  advance. 

Fig.  722  is  an  example  of  combined  inertia  and  neutralized  centrifugal 
control  with  variable  angular  advance  regulation. 

It  should  be  understood  that  the  series  of  illustrations,  figs.  717  to  722, 
are  intended  to  represent  principles  rather  than  construction,  and  are 
therefore  to  be  regarded  as  elementary  diagrams. 


Figs.  723  and  724. — Mcintosh  and  Seymour  governor  in  forward  and  reverse  motion.  In 
operation,  centrifugal  force  throws  the  weights  2  and  3,  outward  giving  variable  angular 
advance. 


Figs.  725  and  726. — Buckeye  governor  in  forward  and  reverse  motion.  Centrifugal  control 
and  variable  angular  advance  regulation.  To  reverse,  all  connections  are  put  in  opposite 
places. 


GOVERNORS 


397 


Auxiliary  Devices. — Some  governors  are  fitted  with  dash 
pots  or  other  damping  devices  to  prevent  super-sensitiveness. 
All  governors  should  be  provided  with  a  safety  stop,  or  device 


Figs.  727  and  728. — Clark  combined  centrifugal  and  inertia  governor  in  forward  and  reverse 
motion.  Regulation  is  by  variable  angular  advance.  The  centrifugal  weights  2  and  3  are 
pivoted  at  4  and  5  respectively.  Inertia  control  is  secured  by  the  weight  7  pivoted  radially 
at  6. 


Figs.  729  and  730. — Russell  centrifugal  governor  in  forward  and  reverse  motion.  Regulation 
is  by  variable  angular  advance.  To  reverse  this  engine  the  main  eccentric  must  be  turned,  and 
if  an  offset  key  be  used  it  must  be  reversed.  The  cut  off  eccentric  must  be  carried  around 
on  the  shaft  until  it  has  the  same  angular  position  in  advance  of  the  crank  that  it  had  before. 
It  is  necessary  to  reverse  the  spring  connections  and  weighted  arms  to  accomplish  this.  The 
eccentrics  are  made  in  halves  to  facilitate  their  removal. 


398 


GOVERNORS 


which  closes  the  throttle  in  case  the  belt  or  drive  gear  should 
break.  A  desirable  feature  is  a  speed  regulator  which  permits 
wide  adjustment  of  the  speed  during  operation. 

These  devices  are  illustrated  in  the  various  cuts  of  governors 
as  constructed  by  the  various  manufacturers. 


Fig.  731. — Variable  speed  changing  cones  as  applied  to  the  Ball  variable  speed  engine.  In 
operation,  the  speed  of  the  upper  cone  is  constant  while  that  of  the  lower  (together  with 
the  engine  speed),  varies  as  the  cone  belt  is  shifted  to  the  right  or  left  by  means  of  the  shifter 
operated  by  the  hand  wheel. 

Variable  Speed  Governors. — There  are  some  conditions  of 
service,  as  in  paper  mills,  where  it  is  frequently  necessary  to 
vary  the  speed  of  the  engine  within  a  wide  range.  Engines 
fitted  with  governors  designed  especially  for  speed  variations 
are  known  as  variable  speed  engines,  and  are  intended  for  all 
classes  of  manufacturing  where  the  quality,  thickness  or  weight 


GOVERNORS 


399 


uf  the  raanufactured  product  is  affected  by  the  speed  at  which 
the  machinery  runs.  The  governor  is  usually  of  the  throttle 
type  fitted  with  a  pair  of  variable  speed  cones  as  shown  in 
fig.  731,  or  with  friction  discs  as  in  fig.  732. 

Since  the  speed  of  the  governor  must  always  he  constant y  no  matter 
what  speed  is  required  of  the  engine,  evidently  the  speed  changing 


Fig.  732.— American  Ball  variable  speed  mechanism  and  automatic  stop  as  applied  to  paper 
mill  engine.  At  the  left  in  the  rear  is  the  speed  ^governpr  driver  through  variable  speed 
friction  discs,  and  at  the  right,  the  automatic  engine  stop  driven  directly  from  the  engine. 
The  steam  valve  of  the  automatic  stop  remains  wide  open  throughout  the  whole  normal 
range  of  speeds  for  which  the  engine  is  designed,  but  in  case  the  speed  exceed  the  prede- 
termined limit,  the  mechanism  is  tripped  and  the  weighted  lever  closes  the  steam  valve. 
At  all  speeds  within  range  of  the  variable  speed  device,  the  automatic  stop  has  no  throttling 
effect  and  hence  cannot  affect  the  speed  of  the  engine. 

part  of  the  mechanism  is  some  form  of  transmission  between  the 
engine  shaft  and  the  governor  by  means  of  which  the  ratio  of 
gearing  may  be  varied,  just  as,  for  instance,  is  done  in  the 
transmission  or  gear  box  of  an  automobile,  only  in  the  case  of  the 
variable  speed  governor,  there  must  be  possible  an  infinite 
number  of  gradations,  or  speed  changes,  instead  of  three  or  four 
as  in  the  automobile. 


400  GOVERNORS 


Referring  to  the  principle  just  stated,  there  is  a  speed  stamped  on  every 
throttling  governor  and  the  valve  of  the  governor  will  not  close  until  that 
speed  is  reached.  Different  sizes  and  styles  of  governors  are  stamped  for 
different  speeds,  but  the  same  principle  applies  to  all. 

To  illustrate  this,  if  the  governor  of  an  ordinary  throttling  engine  were 
stamped  at  200  revolutions,  and  it  was  required  to  run  the  engine  at  100 
revolutions,  it  would  be  necessary  to  put  a  governor  belt  pulley  on  the 
governor  shaft  one-half  the  diameter  of  the  governor  belt  pulley  on  the 
engine  shaft,  that  is,  the  diameter  of  the  two  pulleys  would  have  to  be  such 
that,  when  the  engine  was  running  at  100  revolutions  the  governor  would 
be  running  at  200  revolutions;  because,  as  stated,  the  governor  will  not 
regulate  the  steam  supply  until  it  has  reached  the  speed  which  the  manu- 
facturers stamp  upon  it. 

In  showing  how  this  principle  is  applied  with  variable  speed  cones,  as 
in  fig.  731,  it  must  be  remembered  that  the  upper  cone  of  the  pair  always 
runs  at  a  constant  speed  because  the  governor  runs  at  a  constant  speed; 
the  governor  shaft  and  the  upper  cone  being  geared  together.  With  this 
in  mind,  suppose  that  the  short  belt  connecting  the  two  cones  is  so  placed 
that  it  is  at  the  big  end  of  the  lower  cone,  and  consequently,  is  at  the  small 
end  of  the  upper  cone.  Under  these  conditions,  the  engine  would  run  at 
a  very  slow  speed. 

The  reverse  of  this  situation  would  occur  when  the  short  belt  between 
the  cones  is  shifted  to  the  small  end  of  the  lower  cone,  and  consequently 
is  at  the  large  end  of  the  upper  cone.  Under  these  conditions,  the  engine 
would  run  very  fast,  in  order  to  keep  the  speed  of  the  governor  at  the  speed 
stamped  upon  it. 

This  belt,  which  connects  the  two  cones,  is  held  in  a  frame,  and  this 
frame  is  moved  from  one  extreme  of  the  cone  to  the  other,  by  means  of  a 
long  screw  turned  at  the  end  by  a  hand  wheel.  This  hand  wheel  is  shown 
in  the  figure  at  the  right  of  the  open  engine.  By  turning  this  wheel,  the 
belt  is  gradually  moved  along  the  cones,  from  one  end  to  the  other,  and 
this  movement  causes  the  engine  to  run  at  varying  speeds  in  order  that 
the  governor  may  always  run  at  the  constant  speed  stamped  on  it. 

By  means  of  this  device  it  will  be  seen  that  the  speed  of  the  engine  is 
regulated  with  the  utmost  nicety,  increasing  or  decreasing  gradually  and 
without  the  slightest  shock  to  the  driven  machinery,  and  without  shutting 
the  engine  down.  Since  the  cones  are  tapered  instead  of  being  stepped, 
the  number  of  possible  changes  between  the  two  extremes  is  without  limit. 

If  it  be  desired  to  regulate  the  speed  of  the  engine  from  some  other  part 
of  the  room,  the  hand  wheel,  which  operates  the  screw  of  the  regulating 
device,  may  be  replaced  by  a  sprocket  wheel  and  chain. 

Usually  a  graduated  scale  and  pointer  are  provided  on  the  speed  changing 
device,  so  that  the  engine  may  be  set  to  run  at  any  desired  speed,  or  changed 
from  one  soeed  to  another,  without  using  a  speedometer. 


GOVERNORS 


401 


Since  a  variable  speed  engine  usually  operates  machinery 
worth  many  times  the  value  of  the  engine,  a  secondary  speed 
control  is  provided,  which .  provides  additional  means  of  pre- 
venting damage  to  the  driving  machinery  in  case  of  accident. 

One  type  of  secondary  speed  control  consists  of  a  quick  closing  emergency 
stop  valve  in  the  steam  line,  which  is  automatically  closed  by  a  tripping 
device,  attached  to  the  rim  of  the  band  wheel.  This  tripping  device  flies 
out  under  high  speeds  and  releases  a  catch  which  is  connected  by  a  rod  to 


Pig.  733. — Chandler  and  Taylor  trigger  device  for  secondary  speed  control.     In  .operation^ 

when  the  speed  of  the  engine  exceeds  a  predetermined  rate,  centrifugal  force  causes  the  lever 
A,  pivoted  at  B,  to  overcome  the  compression  of  the  spring  C,  and  fly  out  engaging  the 
trip  D,  pivoted  at  E,  which  releases  the  steam  arm  F,  allowing  the  weight  W  to  fall  and 
close  the  butterfly  valve  V. 

the  weight  lever  of  the  emergency  stop  valve.  When  released  this  weight 
on  the  lever  of  the  valve  swings  to  its  lowest  position  and  shuts  off  the 
steam. 

A  second  type  of  secondary  speed  control  is  the  shaft  governor  connected 
to  a  swinging  eccentric  and  so  developed  that  it  will  not  become  operative 
until  the  speed  of  the  engine  arrives  at  the  maximum  speed  at  which  it  is 
to  run.  Any  effort  of  the  engine  to  run  beyond  this  maximum  speed 
shortens  the  valve  travel  and  by  so  doing  cuts  off  the  stearn  in  the  steam 
chest.  In  this  device  the  engine  is  not  brought  to  a  stop  as  with  the  trigger 
device.  In  this  second  plan  the  engine  operates  at  its  maximimi  spee4» 
until  it  is  shut  down  by  hand. 


402  GOVERNORS 


The  objection  to  the  trigger  device  is  not  in  the  device  itself,  but  in  the 
neglect  of  it.  If  the  trigger  in  the  wheel  be  not  kept  clean  and  free  it  is 
apt  to  gum  up  and  stick,  and  thus  fail  to  perform  its  functions,  when  called 
on  to  do  so.  The  only  objection  to  the  shaft  governor  device  is  its  increased 
expense.  There  ai^  no  pins  to  stick  in  the  shaft  governor,  and  the  weights 
in  the  wheels,  rotating  at  the  high  speeds  which  they  do,  have  sufficient 
power  to  take  care  of  any  emergency. 

In-  the  operation  of  paper  machines  the  shaft  governor  has  still  another 
advantage:  When  the  engine  speeds  up  to  its  maximum  speed,  the  operator 
can  tear  off  the  line  of  paper  at  a  point  before  it  enters  the  drying  rolls, 
and  so  allow  the  paper  in  the  dryers  to  run  itself  out  and  clear  the  machine 
before  engine  is  shut  down. 

With  the  trigger  device  the  engine  is  shut  down  at  once,  leaving  all 
the  paper  in  the  machine. 

Governor  Troubles. — A  governor  with  its  delicate  control 
and  regulating  mechanism  is  a  delicate  piece  of  apparatus  and 
must  be  kept  in  first  class  condition  to  secure  satisfactory 
working. 

Dry  pins  often  give  trouble  by  introducing  excess  friction  which  opposes 
the  controlling  force.  As  much  alteration  should  be  given  to  governor 
lubrication  as  to  any  other  part  of  the  engine.  Special  attention  should  be 
given  to  the  lubrication  of  eccentrics,  and  the  main  pin  on  inertia  governors. 

Lost  motion  in  the  various  joints  is  not  conducive  to  best  operation. 

The  engineer  should  frequently  move  the  governor  weight  arms  by 
hand  when  the  engine  is  not  running;  any  undue  force  required  in  this 
operation  on  small  and  medium  size  engines  will  indicate  that  some  part 
of  the  apparatus  is  not  in  proper  working  order. 

Every  time  the  valve  stem  packing  is  tightened  more  resistance  is  added 
which  must  be  overcome  by  the  controlling  force,  hence  for  satisfactory 
governor  operation  the  valve  stem  packing  should  be  kept  in  as  near  one 
adjustment  as  possible. 

The  valve  setting  or  its  condition  is  quite  as  important  as  other  causes 
of  trouble.  See  if  the  valve  be  set  properly  or  if  it  leak,  or  the  pressure 
plate  bind. 

If  the  normal  load  be  such  that  the  valve  does  not  over  travel  the  seat, 
a  shoulder  will  be  worn  near  the  seat  limit,  hence  a  slight  increase  of  load 
causing  more  travel  will  cause  the  valve  to  ride  on  the  shoulder  and  leak. 
The  valve  seat  should  be  carefully  examined  for  this  defect. 

When  springs  are  too  weak  to  give  the  required  tension,  cut  off  enough 
'  turns  to  produce  the  proper  effect. 


PUMP  VALVE  GEARS  403 


CHAPTER  12 
PUMP  VALVE  GEARS 


Principles  of  Operation.: — Many  ingenious  valve  gears  have 
been  devised  for  operating  the  steam  ends  of  direct  acting  pumps. 
The  need  for  such  special  devices  is  caused  by  the  absence  of  a 
rotating  part  which  prevents  the  use  of  an  eccentric.  In  most 
cases,  the  necessary  movements  of  the  valve  gear  are  obtained 
from  two  sources : 

1.  The  movement  of  the  piston  or  piston  rod; 

2.  The  steam  pressure. 

The  valve  gear  when  thus  operated  usually  consists  of: 

1.  A  main  slide  valve  which  admits  and  exhausts  steam  from 
the  cylinder; 

2.  An  auxiliary  piston  connected  to  the  main  valve  and  moving 
in  a  cylinder  formed  in  the  valve  chest ; 

3.  An  auxiliary  valve  controlling  the  steam  distribution  to 
the  auxiliary  piston  cylinder,  and  operated  with  suitable  gear 
by  the  main  piston,  or  piston  rod. 

The  cycle  of  operation  of  a  valve  gear  of  this  type  is  as  follows : 

As  the  main  piston  approaches  the  end  of  the  stroke,  it  moves 
the  auxiliary  valve  which  causes  steam  to  be  admitted  to  one 
end  of  the  auxiliary  piston  and  exhausted  from  the  other.  This 
results  in  a  movement  of  the  auxiliary  piston  which  in  turn 


404 


PUMP  VALVE  GEARS 


W^ 


Figs.  734  and  735. — Valve  gear  of  the  Snow  pump.  The  auxiliary  valve  is  a  plain  flat  slide 
operated  by  a  valve  stem,  the  latter  being  moved  back  and  forth  by  means  of  a  rocker  shaft, 
as  shown,  the  upper  end  of  which  alternately  comes  in  contact  with  the  collars  on  the  stem. 
Tlie  outer  end  of  the  valve  stem  passes  through  a  sleeve  attached  to  a  pin  in  the  upper  end 
of  the  rocker  arm,  as  shown.  A  knuckle  joint  near  the  stuffing  box  permits  the  rod  to  vibrate 
without  causing  any  derangement  in  the  alignment  of  valve  stem  through  the  stuffing  boxes. 
On  the  valve  stem  at  either  end  of  the  auxiliary  valve  is  a  spring,  which  tends  to  keep  the 
valve  in  a  central  position,  so  that  when  the  rocker  arm  engages  one  of  the  collars,  the  valve 
IS  drawn  against  the  spring  toward  that  end  of  the  stroke.  The  result  is  that  the  stem  and 
valve  follow  the  rocker  arm  on  the  return  stroke  to  its  mid-position,  and  are  started  on  the 
latter  half  of  the  stroke  by  the  stem,  but  without  shock  or  lost  motion.  This,  arrangement  is 
particularly  valuable  in  the  case  of  condensers,  and  in  pumps  where  the  first  part  of  the  stroke 
IS  made  quickly,  and  the  piston  is  then  suddenly  stopped  by  coming  in  contact  with  a  solid 
body  of  water,  the  latter  part  of  the  stroke  being  made  much  more  slowly.  The  springs  on 
either  side  of  the  auxiliary  valve  take  up  lost  motion  and  keep  the  parts  in  contact,  thus 
preventing  shocks  and  unnecessary  wear. 

The  auxiliary  valve  controls  the  admission  and  exhaust  of  steam  from  the  steam  chest  and 
valve  piston  in  the  manner  common  to  all  slide  valve  engines.  The  valve  piston  is  con- 
nected to  the  main  valve,  which  allows  the  valve  to  find  its  own  bearings  on  the  seat  and 
not  only  takes  up  the  wear  automatically,  but  produces  even  wear. 

To  set  the  auxiliary  valve,  see  that  the  valve  is  in  its  central  position  when  the  rocker 
arm  is  plumb,  and  that  the  collars  on  the  valve  stem  are  located  at  equal  distances  from 
each  end  of  the  sleeve.  When  the  piston  moves  to  one  end  of  the  stroke,  the  auxiliary  valve 
will  open  the  small  port  at  the  opposite  end,  provided  the  collars  on  the  valve  stem  have  been 
properly  placed.  Setting  the  collars  closer  together  shortens  the  stroke  of  the  piston,  and 
moving  them  farther  apart  lenghens  the  stroke.  The  piston  should  always  make  a  full  stroke 
without  danger  of  striking  the  cylinder  heads. 


PUMP  VALVE  GEARS 


405 


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406 


PUMP  VALVE  GEARS 


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Figs.  738  to  742. — ^Valve  gear  of  the  Deane  pump.  The  main  valve  is  operated  by  a  valve 
piston  without  lost  motion,  as  in  fig.  738.  Steam  is  admitted  alternately  to  opposite  ends  of 
the  valve  piston.  The  motion  of  the  piston  valve  is  controlled  by  a  secondary  valve,  which 
admits  and  exhausts  the  steam  to  the  valve  piston  through  the  small  ports  at  the  sides  of 

Figs.  736  and  737— Continued. 

tappets,  M  M,  which  causes  the  piston  valve  to  start,  after  which  steam  will  complete  the 
work.  When  the  pump  is  running,  the  cross  head  I,  never  quite  touches  the  tappets,  M 
M,  because  it  engages  the  tappets  L  L,  admitting  steam  to  the  piston  valve  and  shifts  it 
before  the  tappets,  M  M,  are  touched.  The  reason  of  the  double  ports  in  the  aijxiliary 
steam  ch«st  is  to  have  one  port  D,  for  steam,  and  one  port  N,  for  the  exhaust.  Steam 
being  imprisoned  between  these  two  ports  forms  a  cushion,  preventing  the  piston  valve 
striking  the  heads  of  the  chest.  The  tappets  L  L,  set  closer  together  or  farther 
apart  control  the  stroke  of  the  main  piston  H.  When  the  pump  is  running  very  fast,  the 
momentum  of  the  moving  parts  increases  and  the  tappets  will  have  to  be  set  closer  together 
for  high  speed  than  for  slow.  The  tappets  M  M,  are  adjustable  to  their  right  relation  with 
the  tappets  L  L.  The  general  design  and  easy  means  of  adjustment  make  a  reliable  single 
cylinder  valve  motion. 

To  set  the  values. — There  are  no  complicated  internal  parts  requiring  adjustment,  and 
almost  all  parts  requiring  manipulation  can  be  handled  while  the  pump  is  running. 


PUMP  VALVE  GEARS  407 


moves  the  main  valve.  The  steam  distribution  to  the  main 
cylinder  thus  affected,  reverses  the  motion  of  the  main  piston, 
and  the  return  stroke  takes  place,  completing  the  cycle. 

In  pumps  of  different  makes,  the  detail  which  varies  mostly 
is  the  auxiliary  valve  and  the  method  by  which  it  is  operated. 
With  respect  to  these  features  the  majority  of  pumps  may  be 
divided  into  two  classes,  as  those  having: 

1.  A  separate  auxiliary  valve; 

2.  Auxiliary  valve  and  auxiliary  piston  combined. 

In  pumps  of  the  first  mentioned  type,  the  auxiliary  valves 
usually  have  stems  or  tappets  which  project  into  the  cylinder  at 
the  ends  and  are  moved  by  contact  with  the  raain  piston  as  it 
nears  the  end  of  the  stroke. 


Figs.  738  to  7 ^^2— Continued, 

the  steam  chest.    The  secondary  valve  derives  its  motion  from  the  valve  stem,  tappets,  links 
and  the  piston  rod  as  shown.  _ 

In  operation,  assume  the  piston  moving  in  the  direction  of  the  arrow  near  the  end  of  the 
stroke ;  the  tappet  block  comes  in  contact  with  the  left  hand  tappet  and  throws  the  secondary 
valve  to  the  left  until  its  edge,  A,  fig.  741,  uncovers  the  small  port,  S,  figs.  739  and  740, 
admitting  steam  to  the  valve  piston.  The  port,  E,  and  chamber,  F,  in  the  secondary  valve 
5)rovide  for  the  exhaust  of  steam  from  the  left  hand  end  of  valve  piston  in  the  same  manner 
and  at  the  same  time  that  steam  is  admitted  behind  the  right  hand  end.  The  exhaust  ports 
in  the  chest  allow  for  properly  cushioning  the  valve  piston.  The  small  ports  on  the  other 
side  of  the  steam  cylinder,  figs.  739  and  740,  control  the  motion  of  the  valve  in  the  other 
direction  and  act  in  exactly  the  same  manner  as  those  just  described.  In  case  the  steam 
pressure  should  fail  to  start  the  valve  piston  in  time,  a  lug.  B,  fig.  738.  whicii  forms  apart 
of  the  valve  stem,  comes  in  contact  with  the  valve  piston  and  the  entire  power  of  the  steam 
cylinder  starts  it.  The  correct  timing  of  the  valve  movements  is  controlled  by  the  position  , 
of  the  tappets.  If  they  be  too  near  together,  the  valve  will  be  thrown  too  soon  and  thus 
the  stroke  of  the  pump  will  be  shortened,  while  on  the  other  hand,  if  too  far  apart,  the  pump 
will  complete  its  stroke  without  moving  the  valves.  These  tappets  are  set  and  keved  securely 
before  leaving  the  factory  The  exhaust  from  the  cylinder  is  cut  off  when  the  piston  covers 
the  inner  port,  and  forms  a  steam  cushion  for  the  piston  to  prevent  it  striking  the  heads. 
To  set  the  valve  — Place  the  steam  piston  at  the  end  of  stroke  nearest  stuffing  box  and 
the  secondary  valve  so  that  it  will  uncover  the  steam  port,  S,  figs.  739  and  740.  Set  the  tappet 
next  to  the  steam  cylinder  on  the  valve  stem  against  the  tappet  block  and  secure  it  in  this 
position.  Slide  the  secondary  valve  forward  until  the  opposite  steam  port  is  uncovered 
and  place  the  steam  piston  in  its  extreme  outward  position,  then  set  the  other  tappet 
against  the  tappet  block.  Now  set  the  valve  so  that  the  inside  main  steam  port  is  open 
and  the  valve  piston  in  position  to  engage  the  main  steam  valve,  put  the  valve  chest  on 
the  cylinder  and  secure  it  in  place.  The  pump  will  then  be  ready  to  start  on  the  admission 
of  steam  to  the  steam  chest.  If  when  steam  is  turned  on,  the  pump  refuse  to  start,  simply 
move  the  valve  rod  by  hand  to  the  end  of  its  stroke  and  the  pump  will  move  without 
trouble.  In  renewing  the  packing  between  the  steam  chest  and  cylinder,  caution  should 
be  observed  to  cut  out  openings  for  the  small  ports. 


408 


PUMP  VALVE  GEARS 


Where  the  auxiliary  valve  is  combined  with  auxiliary  piston, 
an  initial  rotary  motion  is  given  the  latter  by  the  external  gear, 
causing  it  to  uncover  ports  which  give  the  proper  steam  dis- 
tribution for  its  linear  movement. 

An  example  of  the  separate  auxiliary  valve  type  is  shown  in 
fig.  743  which  illustrates  the  steam  end  of  the  Cameron  pump. 


Fig.  743. — ^Valve  gear  of  the  Cameron  pump;  an  example  of  the  separate  auxiliary  valve  class.  . 
Its  construction  and  operation  is  explained  in  detail  in  the  accompanying  text.  No  valve 
setting  is  necessary,  it  being  only  necessary  to  keep  the  valves  1,1,  tight  by  occasional 
grinding.  In  operation,  the  piston  as  it  nears  the  end  of  each  stroke  strikes  the  stem  and 
lifts  the  valve  off  its  seat;  this  allows  the  exhaust  steam  behind  the  piston  valve  to  escape. 
The  live  steam  pushes  the  piston  towards  the  exhausted  end  carrying  the  main  slide  valve 
along  with  it. 


Each  auxiliary  valve  I,  has  a  short  stem  which  projects  into 
the  cylinder;  when  the  piston  C,  strikes  one  of  these,  the  valve 
is  driven  back,  and  opens  an  exhaust  passage  E,  from  the 
corresponding  end  of  the  auxiliary  piston  F,  which  immediately 


PUMP  VALVE  GEARS 


409 


Figs.  744  to  748. — ^Valve  gear  of  the  Knowles  pump.  The  valve  piston  is  driven  alternately 
backward  and  forward  by  the  pressure  of  steam,  carrying  with  it  the  main  valve,  which 
admits  steam  to  the  main  steam  piston  that  operates  the  pump.  The  main  valve  is  a  plain 
slide  whose  section  is  of  B  form,  working  on  a  flat  seat.  The  valve  piston  is  slightly  rotated 
back  and  forth  by  the  rocker  bar  H;  this  rotative  movement  places  the  small  steam  ports 
D,  E,  F,  figs.  746  to  748,  which  are  located  in  the  under  side  of  the  valve  piston  in  proper 
position  with  reference  to  the  corresponding  ports  A,  B,  cut  in  the  steam  chest.  Steam 
enters  through  the  port  at  one  end  and  fills  the  space  between  the  valve  piston  and  the  head, 
drives  the  valve  piston  to  the  end  of  its  stroke  and  carries  the  main  slide  valve  with  it. 
When  the  valve  piston  has  traveled  a  certain  distance,  a  corresponding  port  in  the  opposite 
end  is  uncovered  and  steam  enters,  stopping  its  progress  by  giving  it  the  necessary  cushion. 
There  is  no  dead  center. 

In  operation,  the  piston  rod  with  its  tapped  arm  J,  fig.  744,  moves  backward  and  for- 
ward with  the  piston.  At  the  lower  part  of  this  tappet  arm  is  attached  a  stud  or  bolt  K,  on 
which  is  a  friction  roller  I.  This  friction  roller,  lowered  or  raised,  adjusts  the  pump  for  a 
longer  or  shorter  stroke.  This  roller  coming  in  contact  with  the  rocker  bar  at  the  end  of 
each  stroke,  and  this  motion  is  transmitted  to  the  valve  stem,  causing  the  valve  to  roll 
slightly.  _  This  action  opens  the  ports,  admits  steam  and. moves  the  valve  piston,  which 
carries  with  it  the  main  slide  valve  which  admits  steam  to  the  main  piston.  The  upper  end 
of  the  tappet  arm  does  not  come  in  contact  with  the  tappets  L,  M,  on  the  valve  rod,  unless 
the  steam  pressure  from  any  cause  should  fail  to  move  the  valve  piston,  in  which  case  the 
tappet  arm  moves  it  mechanically. 

To  set  the  valve,  loosen  the  set  screws  in  the  tappets  on  the  valve  stem.  Then  place  the 
piston  at  mid-stroke,  and  have  the  rocker  bar  H,  in  a  horizontal  position,  as  shown  in  the 
engraving.  The  valve  piston  should  then  occupy  the  position  shown  in  fig.  748.  The 
valve  piston  may  be  rotated  slightly  in  order  to  obtain  this  position  by  adjusting  the  length 
of  connection  between  the  rocker  bar  H,  and  the  valve  stem.  Then  turn  the  valve  piston 
G,  one  way  or  the  other  to  its  extreme  position,  put  on  the  chest  cover,  and  start  the  pump 
slowly.  If  the  pump  make  a  longer  stroke  on  one  end  than  on  the  other,  lengthen  or  shorten 
the  rocker  connection  so  that  the  rocker  bar  H,  will  touch  the  rocker  roller  I,  equally  distant 
from  the  center  pin  J.       If  the  pump  hesitate  on  the  return  stroke,  it  is  because  the  rocker 


410  PUMP  VALVE  GEARS 

is  shifted  under  the  action  of  Hve  steam  on  the  opposite  side 
of  the  piston  head. 

There  is  a  small  hole  in  each  end  of  the  auxiliary  piston, 
and  when  both  auxiliary  valves  are  closed,  the  steam  passing 
through  these  holes  leaves  the  auxiliary  piston  entirely  sur- 
rounded by  live  steam,  and  therefore  in  perfect  balance  end- 
wise, until  the  main  piston  strikes  the  stem  in  the  opposite 
cylinder  head,  when  the  valve  moving  operations  are  repeated 
in  the  opposite  direction. 

The  space  back  of  the  auxiliary  valve  communicates  with 
the  steam  chest,  through  a  passage  shown  in  dotted  lines;  the 
valve  is  therefore  closed  by  steam  pressure  as  soon  as  the 
piston  moves  back  from  the  stem. 

It  should  be  noted  that  the  piston  closes  the  exhaust  passage  before  the 
end  of  the  stroke.  The  confined  steam  forms  a  cushion  between  the  piston 
and  the  cyHnder  head,  but  a  Httle  passage  is  cut  in  the  cylinder  wall  through 
which  sufficient  stea^n  is  admitted  to  start  the  piston  on  the  return  stroke. 

The  auxiliary  piston  which  carries  the  main  valve  G,  shifts  the  latter  in 
the  direction  the  piston  travels  at  the  end  of  the  stroke,  that  is,  opposite 
to  that  of  a  common  slide  valve.  This  valve  has,  therefore,  two  cavities, 
each  of  which  alternately  puts  the  cyhnder  in  communication  with  the 
steam  chest  and  the  central  exhaust  port.  Steam  is  admitted  under  the 
outer  valve  face,  as  shown  in  the  figure. 

H,  is  a  lever,  by  means  of  which  the  auxiliary  piston  may  be  reversed  by 
hand  when  expedient. 

An  example  of  the  second  mentioned  type  in  which  the 
auxiliary  valve  and  auxiliary  piston  are  combined  is  shown  in 
figs.  753  to  755,  illustrating  the  valve  gear  of  the  Davidson  pump. 


Figs.  744  tp  7 ^S.— Continued. 

roller,  I,  is  too  low  and  does  not  come  in  contact  with  the  rocker  bar,  H,  soon  enough.  To 
raise  it,  take  out  the  rocker  roller  stud,  K,  give  the  set  screw  in  this  stud  a  sufficient  down- 
ward turn,  and  the  stud  with  its  roller  may  at  once  be  raised  to  its  proper  height.  If  the 
valve  rod  tremble,  slightly  tighten  the  valve  rod  stuffing  box  nut.  When  the  valve  motion 
is  properly  adjusted  the  vertical  arm  should  not  quite  touch  the  collar  L,  and  the  clamp  M. 
Rocker  roller  I,  coming  in  contact  with  the  rocker  bar  H,  reverses  the  stroke. 


PUMP  VALVE  GEARS 


4U 


COMBINED  MOVABLE  SEAT 
AND  AUXILIARY  VALVE 


BLAKE  SrtMGLE  PUMP 

SECTIONAL  VIEW 

OF 
STEAM  END 


Figs.  749  to  752. — ^Valve  gear  of  the  Blake  pump.  The  main  valve,  is  carried  by  the  auxiliary 
piston,  and  moves  on  the  back  of  the  movable  seat  (fig.  752),  the  passages  A  B  C,  of  which 
serve  as  steam  passages.  The  lugs  G  G',  control  admission  of  steam  to  the  auxiliary  cylinder, 
and  the  holes  H  H',  control  the  exhaust  from  that  cylinder.  In  operation,  when  the  piston 
nearly  reaches  the  left  end 'of  the  cylinder,  the  movable  seat  is  shifted  to  the  left  so  that  lug 
G,  covers  the  port  E,  while  lug  G',  uncovers  port  E',  thus  admitting  steam  behind  the  auxiliary 
piston  at  the  left  side.  At  the  same  time  the  exhaust  port  K,  of  the  auxiliary  cylinder  is 
opened  to  the  hole  S,  leading  to  the  exhaust,  and  forcing  the  auxiliary  piston  over  to  the  right, 
uncovering  port  A,  to  live  steam.  Near  completion  of  the  stroke  the  operation  is  reversed. 
The  auxiliary  piston  is  cushioned  on  steam,  because  the  exhaust  port  is  not  out  at  the  end 
of  the  auxiliary  cylinder,  and  consequently  there  is  steam  imprisoned  when  the  piston  covers 
the  exhaust,  as  at  the  left  in  fig.  751.  The  main  piston  is  cushioned  on  live  steam,  because 
the  valve  has  lead;  that  is  the  operation  of  admitting  steam  is  performed  before  the  piston 
reaches  the  end  of  its  stroke.  It  will  be  seen  that  if  means  be  provided  to  shift  the  movable 
seat  from  one  end  of  its  travel  to  the  other,  the  rest  of  the  operation  is  automatic.  Fig.  752, 
shows  the  valve  gear  provided  for  this  operation.  The  piston  rod  is  provided  with  a  cross 
head,  the  latter  having  a  pin  as  shown.  The  frame  of  the  pump  is  built  with. an  upright 
piece  U,  to  which  is  pivoted  at  P,  a  lever  whose  lower  end  is  slotted  and  engages  with  the 
cross  head.  The  valve  rod,  which  is  secured  to  the  movable  seat,  is  provided  with  two  collars 
as  shown.  These  collars  are  made  of  split  nuts  which  work  on  a  thread  cut  on  the  valve  rod 
for  a  short  distance  on  each  side  of  their  ordinary  position.  Between  these  two  collars  is  a 
tappet,  which  is  free  to  slide  on  the  valve  rod.    The  link  shown  connects  the  tappet  with  the 


412  PUMP  VALVE  GEARS 


The  main  valve  is  operated  by  a  positive  mechanical  connection  between 
it  and  the  main  piston  rod,  also  by  the  action  of  steam  on  the  valve  pistons. 
Fig.  753,  shows  the  details  of  valve  gear  and  steam  cylinder.  In  the  fig- 
ures the  steam  end  consists  of  the  cylinder  M,  valve  A,  and  valve  pistons 
B  and  B.  These  pistons  are  connected  with  sufficient  space  between  them 
for  the  valve  A,  covering  the  steam  ports  P  and  Fi,  as  in  fig.  755. 

The  valve  is  operated  by  the  steel  cam  C,  acting  on  a  steel  pin  D,  which 
passes  through  the  valve  into  the  exhaust  port  N,  in  which  the  cam  is 
located.  In  addition  to  this  positive  motion,  steam  is  alternately  admitted 
to  and  exhausted  from  the  ends  of  the  valve  piston  through  the  ports  E 
and  El,  which  moves  the  pistons  B  and  Bi. 

Assuming  the  pump  to  be  at  rest  with  the  valve  A,  covering  the  main 
steam  ports  F  and  Fi,  in  which  position  the  cam  C,  holds  the  main  valve 
by  means  of  the  valve  pin  D,  so  that  ports  E  and  Ei,  admit  steam  to  one 
end  of  the  valve  piston  at  the  same  time  connects  the  other  end  with  the 
exhaust  port.  The  steam,  acting  on  the  valve  pistons,  moves  both,  opening 
the  main  ports  F  and  Fi,  admitting  steam  to  one  end  of  the  steam  cylinder 
and  opening  the  other  end  to  the  exhaust. 

If  the  valve  occupy  any  other  position  than  the  one  described,  the  main 
ports,  F  and  Fi,  will  be  opened  for  the  admission  and  exhaust  of  steam; 
consequently  it  is  evident  that  this  pump  will  start  from  all  points  of  the 
stroke. 

On  the  admission  of  steam  to  the  cylinder  the  main  port  F,  the  main 
piston,  cam  and  valve  will  move  in  the  direction  indicated  by  the  arrows. 
The  first  movement  of  the  cam  oscillates  the  valve,  preparatory  to  bringing 
it  into  a  proper  position  for  the  opening  of  the  auxiliary  steam  ports  E, 
to  live  steam,  and  E,  to  exhaust,  also  to  close  the  valve  mechanically  just 
before  the  main  piston  reaches  the  end  of  its  stroke.    This  causes  a  slight 


Figs.  749  to  752. — Continued. 

lever.  When  the  piston  rod  moves,  the  lever  rotates  about  P,  carrying  the  tappet  with  it; 
and  when  the  tappet  strikes  either  collar  it  moves  the  movable  seat  in  the  direction  in  which 
the  tappet  is  moving.  By  placing  the  collars  so  that  the  tappet  strikes  them  before  the 
piston  reaches  the  end  of  its  stroke,  the  movable  seat  will  be  shifted  in  the  required  manner. 
To  set  the  valves. — No  valve  adjustment  is  required  to  be  made  inside  the  steam  chest, 
and  the  only  adjustment  which  can  be  performed  is  that  of  altering  the  distance  between  the 
collars,  thus  changing  the  travel  of  the  valve.  This  is  done  by  loosening  the  set  screws  in  the 
collars,  and  rotating  the  latter  until  they  come  to  the  required  point.  Changing  the  distance 
between  the  collars  alters  the  length  of  the  stroke.  This  is  easily  seen,  because  the  action 
of  the  tappet  in  striking  the  collars  is  what  admits  and  exhausts  the  steam;  and  if  the 
distance  which  the  tappet  has  to  travel  be  varied,  the  time  at  which  the  valve  is  actuated  is 
varied,  and  the  stroke  varies  as  well.  The  adjustment  of  these  collars  is  very  simple,  and 
can  be  performed  while  the  pump  is  running.  In  adjusting  them  it  is  desirable  to  make  the 
stroke  as  Jong  as  possible  and  secure  enough  cushioning,  for  the  shorter  the  stroke  the  greater 
the  amount  of  the  clearance,  and  the  steam  required  to  fill  the  clearance  is  wasted  on  every 
stroke.  If  the  collars  on  the  valve  rod  be  not  set  at  equal  distances  from  the  center  line  of 
the  lever  when  the  latter  is  vertical,  the  movable  seat  will  be  reversed  sooner  on  one  stroke 
than  on  the  other,  and  consequently  the  piston  will  travel  further  in  one  direction  than 
in  the  other. 


PUMP  VALVE  GEARS 


413 


Figs.  753  to  755. — Valve  gear  of  the  Davidson  pump;  an  example  of  the  combined  auxiliary 
valve  and  auxiliary  piston  class.  To  set  the  valve  piston,  push  the  main  pistons  to  the  end 
of  the  stroke  until  the  inner  edge  of  the  port  and  the  piston  coincide,  then  loosen  the  side 
lever,  turn  the  cam  C,  until  the  valve  piston  uncovers  the  auxiliary  steam  port  E,  leading 
to  the  same  end  of  the  steam  chest  occupied  by  the  main  piston.  After  setting,  secure  the 
cam  and  then  connect  the  side  lever  to  the  connecting  rod.  The  side  lever  and  cam  occupy 
correct  relative  positions,  therefore,  the  lever  should  be  secured  to  the  cam  shaft  while  in 
this  position.  The  stroke  may  be  regulated  by  raising  or  lowering  the  end  of  the  connecting 
rod  in  the  slotted  end  of  the  slide  lever.  Raising  the  connecting  rod  shortens  the  stroke  and 
lowering  it  lengthens  the  stroke.  When  making  the  foregoing  adjustments  it  is  well  to  have 
the  connecting  rod  at  or  near  the  bottom  of  the  slot  as  shown  in  the  engravings. 


414 


PUMP  VALVE  GEARS 


xn 


_S  g  I-  o  p,S-;3 

3  vh  <u  o 

5    rt    r^  -O^ 

7-43  ^'d  S.-t^  d 

:!  I  g  I  >l 

re)    O^ 


a  a  G  S 

03   u 

G   03 


3  <^  (D  ;^ 


13   t/i 
OJ         V^a;    OJ 


o 


03 


^  §  a « 

^  wjg  0.2 
b 


O 


QJ   O   cd  ;zj 


,,  s  a  cu.S  "^ 


I'S  ^'2 


03    ^^O 

cd  0;+^  ^  ^ 

^-^  ^  a  8 

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(D   bJ   ^ 
}H   O   p 


^^.^ 


^^  ^  <D  a 


O^-^    ^    (L>    OS 

^«  6'^  ^S 


ge-i  S'rt 


PUMP  VALVE  GEARS 


415 


The  Duplex  Pump  Valve  Gear.  If  two  steam  pumps  be 
placed  side  by  side,  it  is  found  that  the  main. valve  of  each  may  be 
operated  directly  from  the  piston  rod  of  the  other  without  the 
aid  of  any  auxiliary  pistons  or  valves  as  is  necessary  with  single 


Figs.  758  and  7o9. — Plan  and  elevation  of  one  side  of  a  duplex  ptimp  showing  steam  cylinder 
and  valve  gear. 

pumps.  Each  piston  rod  then  with  suitable  connections  operates 
the  valve  of  the  other  pump  in  such  sequence  that  the  strokes 
are  alternately  made  resulting  in  a  discharge,  nearer  uniform 
than  is  obtained  in  a  single  pump.  Figs.  758  and  759  show 
the  general  arrangement  of  the  valve  gear. 


416 


PUMP  VALVE  GEARS 


The  duplex  pump  has  one  main  valve  for  each  side,  there  being 
no  auxiliary  valves. as  in  single  pumps.  These  main  valves,  as 
shown  in  figs.  760  and  761,  are* nothing  more  than  ordinary  slide 
valves. 

It  will  be  seen  from  fig.  761  that  the  valve  seat  has  five  ports,  giving 
separate  steam  and  exhaust  passages  and  a  central  exhaust  cavity  as  shown. 

The  passages  nearest  the  ends  are  steam  passages  while  the  inner 
passages  are  for  exhaust.    These  inner  passages  are  covered  or  closed  by  the 


H 


Figs.  760  and  761. — Main  valve  and  valve  seat  of  duplex  pump;  each  "side"  or  pump  is  fitted 
with  a  valve  and  seat  as  here  shown.  H  and  F,  are  the  steam  edges  of  the  valve  and  G  and  I, 
the  exhaust  edges.  Q  and  K,  are  the  steam  ports  and  O  and  R,  the  exhaust  ports;  the  exhaust 
cavity  or  outlet  is  seen  at  the  center  of  the  seat.  Fig.  760,  shows  the  lost  motion  between  the 
stem  and  valve.  The  amount  of  lost  motion  given  is  such  that  the  inlet  ports  are  not  closed 
and  the  exhaust  ports  opened  too  early  in  order  to  allow  the  piston  to  make  a  full  stroke. 


piston  just  before  the  end  of  the  stroke  whereby  a  portion  of  the  exhaust 
steam  is  compressed  and  made  to  act  as  a  cushion  between  the  piston  and 
cylinder  head,  thus  preventing  the  piston  striking  the  cylinder  heads  when 
operating  at  high  speed;  this  assists  materially  in  the  operation  of  the 
pump. 

The  travel  of  the  valve  is  such  that  its  exhaust  edge  never  passes  by  the 
steam  edge  of  the  steam  port,  hence  steam  can  only  be  exhausted  through 
the  exhaust  port. 


PUMP  VALVE  GEARS 


417 


In  large  pumps,  a  by- 
pass is  provided,  con- 
necting the  steam  and 
exhaust  ports;  the  by- 
pass is  provided  with  a 
stop  valve  by  means  of 
which  the  compression 
can  be  regulated.  The 
adjustment  of  this 
valve  depends  upon  the 
speed  of  the  pump,  the 
higher  speeds  requiring 
more  compression. 


The  gear  by  which 
the  motion  of  the  piston 
rods  is  reduced  and 
transmitted  to  the 
valves  is  fully  shown 
in  the  accompanying 
cuts.  From  the  illus- 
trations it  is  seen  that 
the  piston  rod  of  each 
cylinder  is  provided 
with  a  cross  head  which 
connects  with  a  rocker 
arm.  This  rocker  arm 
is  attached  to  a  rocker 
shaft,  having  at  the 
other  end  a  short  rocker 
arm,  which  is  con- 
nected with  the  valve 
stem  of  the  other 
cylinder  through  a  con- 
necting link. 

The  valve  stem  is 
not  rigidly  attached  to 
the  valve  but  con- 
siderable lost  motion  is 
given,  as  shown  in  fig. 
762,  so  that  the  valve 
is  not  moved  until  the 
piston  has  reached 
nearly  half  stroke. 


Preliminary    to 


418  PUMP  VALVE  GEARS 

setting  the  valves  of  an  old  pump  it  should  be  ascertained  if  the  cross  heads 
have  shifted  on  the  piston  rods. 

Method  of  Locating  Cross  Head  Centers. — Usually  the 
cross  heads  of  duplex  pumps  are  held  in  position  by  a  pin, 
which  is  driven  through  cross  head  and  rod,  after  the  former  has 
been  adjusted.  It  is  impossible  for  the  cross  head  to  shift  its 
position  accidentally,  unless  the  pin  should  drop  out,  and  even 
then,  there  is  a  set  screw,  holding  the  cross  head  against  slippage 
by  ordinary  use,  and  if  such  a  thing  should  happen,  the  best 
way  to  readjust  is  to  find  its  former  position  by  the  pinhole  in 
the  piston  rod- 


Fig.  763. — ^A  very  small  Worthington  duplex  pump.  Its  dimensions  are  as  follows :  2  inch  dlam. 
steam  cylinder;  l}/^  inch  water  cylinder;  2%  inch  stroke.  Its  capacity  is  .004  gallon  per 
revolution;  rev.  per  minute,  80j  gallons  per  minute,  3.5.  Steam  pipe,  ^  inch;  exhaust  pipe, 
yi  inch;  suction  pipe,  l_inch;  discharge,  %  inch.     Floor  space  occupied,  1'  9"  X  7"  wide. 

Sometimes,  however,  it  is  necessary  to  replace  the  old  piston  rods  by 
'  new  ones,  which  may  be  quite  frequently,  if  the  water  be  bad,  and  steel  rods 
are  used.  In  most  cases  the  engineer  will  find  that  the  rods  can  be  put 
into  their  proper  places  without  any  trouble,  as  the  builders  have  always 
exact  fitting  duplicates  in  stock,  but  it  is  better  to  be  sure  of  this,  by  making 
the  following  test :  Mark  the  extreme  position  of  the  cross  head  on  both 
sides  of  the  pump  on  the  frame  or  on  a  wood  lathe,  wedged  in  between  the 
cylinder  heads  as  shown  in  the  figure. 

If  a  lathe  be  not  used,  the  positions  of  the  cross  heads  may  be  trans- 
ferred to  the  frame,  by  using  a  small  set  square. 

Next  put  a  mark,  on  either  the  frame  or  the  lathe,  to  correspond  with  the 
central  or  mid-stroke  position  of  the  cross  head.  This  may  be  obtained  in 
two  different  ways,  both  being  illustrated  in  figs.  758  and  759. 

The  use  of  the  plumb  bob  as  in  fig.  759  should  only  be  used  if  the  pump 


PUMP  VALVE  GEARS 


419 


^^^^W^^^^ 


mu 


^m2^^^zz^//jm^/^ 


be  leveled  properly, 
while  the  square  may 
be  used  under  any  con- 
dition, providing  the 
piston  rods  be  not 
worn  too  badly. 

When  dropping  the 
plumb  bob  in  line  with 
the  center  of  the  rock 
shaft  as  in  fig.  759,  the 
cross  head  may  be 
moved  close  to  the  line, 
and  its  position  be 
transferred  to  the 
frame  as  in  fig.  758. 

In  the  other  method, 
the  square  is  used 
against  the  hub  of  the 
rocker  arm,  and  thus, 
it  will  be  seen  by 
examining  fig.  759  that 
the  heel  of  the  square 
does  not  indicate  the 
center  of  the  rock  shaft, 
but  is  out  an  amount, 
equal  to  one-half  the 
diameter  of  the  hub  of 
the  rocker  arm,  and 
the  cross  head  should 
therefore  not  be  set 
close  to  the  square, 
but  a  distance,  equal 
to  the  radius  of  the 
hub,  away  from  it. 
This  distance  can  be 
measured  with  an  in- 
side caliper,  or  a  rule, 
and  the  position  of  the 
cross  head  is  then 
transferred  to  the 
frame  as  in  fig.  758,  or 
marked  on  the  lath  as 
shown  in  fig.  764. 

In  both  of  the  above 
methods,  no  marks 
have    been    made   on 


420 


PUMP  VALVE  GEARS 


Figs.  765  to  770. — ^Valve  gear  of  the  Laidlaw-Dunn- Gordon  pump.  The  admission  of  live 
steam  to  the  cyhnder  and  of  exhaust  steam  to  the  atmosphere  is  controlled  by  a  valve  pis- 
ton A,  shown  in  fig.  766.  Assume  that  the  piston  is  in  position  shown,  fig.  769,  and,  that  both  the 


PUMP  VALVE  GEARS  421 


the  piston  rod,  which  is  always  best  to  avoid,  the  cross  head  having  served 
for  a  mark  in  both  cases 

If  the  pump  be  small,  there  is  no  difficulty  to  move  the  pistons  for  this 
purpose,  but  on  a  large  pump,  the  cross  head  may  be  unfastened,  so  as 
to  be  free  to  slide  on  the  piston  rod. 

The  marks  A  A,  representing  the  extreme  positions  of  the  cross  head 
have,  however,  been  taken  from  one  end  of  the  cross  head,  and  thus  can 
not  come  equidistant  from  the  mark  C,  representing  the  correct  central 
position,  even  if  the  cross  head  be  set  correctly.  Thus  it  will  be  necessary 
to  transfer  them  toward  the  opposite  end  of  the  cross  head,  an  amount 
equal  to  one-half  the  length  of  the  cross  head,  B  B,  being  the  corrected 
marks.. 

If  the  position  of  the  marks  B  B,  be  not  equidistant  from  the  center 
mark  C,  when  the  cross  head  is  at  the  extreme  ends  of  the  stroke,  it  should 
be  shifted  on  the  piston  rod,  until  in  the  proper  position,  the  amount  it 
is  to  be  shifted  will  be  indicated  by  the  marks  B  B,  fig.  764. 

It  will  not  be  necessary  to  shift  the  cross  head  on  the  rod,  if  it  be  out 
only  a  small  amount,  as  the  duplex  pump  is  not  such  a  sensitive  machine, 
to  require  very  delicate  adjustment,  and  often  it  is  found,  that,  if  the 


Figs.  765  to  17^.— Continued. 

main  and  auxiliary  valves  cover  their  respective  steam  ports.  By  means  of  a  starting  bar, 
operating  through  a  stuffing  box  in  the  valve  chest,  the  piston  valve  A,  is  moved  toward  the 
head  of  the  steam  chest  D,  thus  opening  the  ports  E  and  L,  and  admitting  live  steam 
through  L,  from  the  cavities  S,  of  the  valve  piston  to  the  housing  end  of  the  main  steam 
cylinder,  through  the  port  F  fig.  769,  forcing  the  main  piston  P,  toward  the  opposite  end 
of  the  stroke,  or  toward  the  left  in  the  figure.  The  port  E,  fig.  453,  being  open,  the  exhaust 
steam  escapes  from  front  of  the  main  piston  through  the  port  F,  fig.  769,  into  the  main 
exhaust  port  G,  through  the  port  E.  The  piston  P,  travels  to  its  extreme  left  position  and 
the  auxiliary  slide  valve  has  been  drawn  to  such  a  position  in  the  direction  indicated  by  the 
arrow  in  the  smaller  drawing  in  fig.  765,  as  to  bring  valve  piston,  A,  toward  the  opposite  end; 
the  exhaust  steam  from  the  steam  chest  escapes  from  before  it,  through  the  exhaust  port  K, 
the  opening  of  which  into  the  chest  is  at  such  a  distance  from  the  head  as  will  permit  sufficient 
exhaust  steam  to  remain  to  afford  a  cushion  to  the  valve  piston.  With  the  auxiliary  slide 
valve  in  position  to  bring  the  hole  H,  over  the  port  J,  fig.  770,  it  is  plain  that  the  exhaust 
through  the  port  K,  will  pass  into  the  main  exhaust  through  the  port  L.  "With  the  main 
piston  at  its  extreme  travel  toward  the  right,  the  ports  E  and  L,  which  correspond  to  F 
and  F,  respectively  in  fig.  769,  are  opened  in  such  a  manner  as  to  exhaust  steam  to  the  at- 
mosphere from  the  housing  end  of  the  steam  cylinder  through  the  port  F,  and  live  steam 
from  the  chest  to  the  head  end  of  the  main  cylinder,  through  the  port  F,  thus  driving  the 
main  piston  P,  toward  the  housing  end  of  the  cylinder,  or  toward  the  right.  The  piston 
and  reciprocating  parts  traveling  in  this  direction  move  the  auxiliary  slide  valve  to  its 
maximum  point  of  travel  in  the  opposite  direction,  thus  opening  the  opposite  auxiliary  steam 
and  exhaust  ports  and  again  driving  the  valve  piston  toward  the  head  D,  of  the  steam 
chest,  whence  a  new  stroke  begins.  Lost  motion  in  the  valve  gear  is  taken  up  by  adjustable 
links,  on  all  sizes  above  7  inches  diameter  by  10  inches  stroke  and  on  some  smaller  sizes. 
Cushioning  of  the  steam  pistons  in  the  larger  sizes  and  upwards  is  accomplished  by  means 
of  suitable  valves  called  cushion  valves.  In  the  smaller  sizes  sufficient  cushioning  is  done 
by  exhaust  steam  passing  from  the  clearance  space  next  the  head  through  a  small  hole  drilled 
into  the  main  steam  port. 

To  set  the  valve  of  this  pump  it  is  only  necessary  to  place  the  piston  in  its  central  position 
and  adjust  the  lever  so  that  the  valve  will  occupy  its  central  position.  By  this  proceeding 
the  travel  of  the  valve  is  equalized. 


422 


PUMP  VALVE  GEARS 


entire  mechanism  be  set  correctly,  the  pump  will  not  work  as  well  under 
steam,  as  if  slightly  out  of  adjustment.* 

If  the  cross  head  be  out  of  adjustment  it  is  advisable  to  test  the  pump 
under  steam,   before  making  alterations.     For  this  purpose  the  valves 


Figs.  771  to  775. — Valve  gear  of 
Dean  Bros.  pump.  The  auxiliary- 
valve,  A,  fig.  771,  has  in  its  face 
two  diagonal  exhaust  cavities, 
B,  Bi.  The  ports,  C  Ci,  and  the  ex- 
haust port,  D,  are  placed  in  a  tri- 
angular position  with  one  another, 
the  diagonal  cavities  diverging  so 
that  the  cavity  B,  when  the  valve 
is  in  place,  connects  the  ports  Ci 
and  D.  Cavity  Bi,  connects  the 
ports  C  and  D,  when  the  valve  A, 
is  at  the  end  of  the  stroke.  The 
three  small  cuts  show  relation  of 
auxiliary  valve  to  ports.  The  pis- 
ton starts  from  left  to  right  when 
the  valve  A,  moves  in  an  opposite 
direction,  opens  the  port  C,  ad- 
mitting steam  to  the  auxiliary 
cylinder  at  the  moment  the  main 
piston  has  reached  the  end  of  its 
stroke.  The  auxiliary  piston  E, 
is  forced  to  the  left,  opening  the 
main  port  and  admitting  steam  to 
the  main  cylinder,  reversing  the 
movement  of  the  main  piston  the 
return  stroke  of  the  main  piston 
reverses  the  movement  of  the  auxiliary  valve,  whereby  the  port  C,  is  closed,  at  the  mo- 
ment the  main  piston  reaches  the  end  of  its  outer  stroke.  The  port  Ci,  is  opened  by  the 
valve  A,  and  reverses  the  valve  piston  E,  opens  the  main  port  and  reverses  the  motion  of 
the  main  piston.  This  port  arrangement  admits  of  a  short  valve  with  a  long  travel.  The 
stroke  of  the  pump  can  be  regulated  by  moving  the  stud  up  or  down  in  the  segmental  slot, 


*NOTE. — If  a  pump  work  better  when  slightly  out  of  adjustment  it  is  due  to  irregularities 
in  the  steam  and  exhaust  ports,  and  is  liable  to  give  more  and  earlier  compression  on  one  end  of 
the  cylinder  than  on  the  other,  and,  when  running  slow,  the  piston  will  not  travel  within  the 
same  distance  from  both  cylinder  heads. 


PUMP  VALVE  GEARS  423 


should  be  adjusted  to  suit  the  original  position  of  the  cross  head,  and  if 
possible,  it  will  be  found  very  useful,  to  attach  a  pointer  to  the  crosshead, 
pointing  toward  that  part  of  the  frame,  on  which  the  center  and  extremes 
of  the  stroke  have  been  marked. 

By  running  the  pump  slow,  it  will  be  possible  to  ascertain  the  ends  of  the 
working  stroke. 

If  the  extreme  positions  of  the  pointer  are  marked,  which  can  be  done  best 
by  holding  a  lead  pencil  against-  the  pointer,  just  touching  the  frame. 
The  points,  to  which  the  lead  pencil  is  pushed  by  the  pointer  on  each  end 
of  the  stroke,  are  the  extremes  of  the  stroke,  when  the  pump  is  running, 
and  by  comparing  these  points  with  the  marks  previously  obtained,  indi- 
cating the  true  ends  of  the  stroke,- the  clearance  on  each  end  can  be  ob- 
tained. 

If  there  be  considerable  difference  in  the  clearance  on  both  ends,  it  is 
best  to  examine  the  valves,  by  moving  the  pistons  by  hand  to  the  extremes 
of  stroke,  as  found  when  running,  and  noting  the  port  opening  at  both  ends, 
for  this  purpose  the  valve  chest  cover  has  to  be  removed. 

If  there  be  any  difference  in  port  opening  at  both  ends,  this  may  be 
the  cause  of  the  unequal  clearance,  and  a  preliminary  valve  adjustment 
should  be  made,  by  equalizing  the  port  opening  approximately  by  eye. 

Various  types  of  pumps  are  provided  with  different  means  for  such 
adjustments,  but  the  principle  remains  the  same,  that  is,  to  either  lengthen 
or  shorten  the  valve  stems,  as  occasion  demands. 

Most  all  types  of  the  smaller  sizes  are  provided  with  the  simple  adjusting 
device,  as  indicated  in  fig.  762  which  consists  of  a  square  nut,  through  which 
the  valve  stem  is  screwed,  and  by  screwing  the  stem  either  in  or  out,  it  is 
respectively  shortened  or  lengthened. 

After  such  a  preliminary  adjustment  has  been  made,  the  pump  should 


Figs.  771  to  lib.— Continued. 

fig.  775,  which  varies  the  travel  of  the  auxihary  valve  and  reverses  the  stroke  of  the  main 
piston  as  desired.  By  raising  the  stud,  the  pump  will  make  shorter  strokes,  and  by 
lowering  it,  longer  strokes. 

To  set  the  valve,  turn  the  steam  chest  upside  down.  Put  valve  stem  through  the  stuffing- 
box  and  secure  in  place  the  clamp  for  small  slide  valve.  The  diameter  of  valve  stem  is  smaller 
where  the  clamp  is  attached.  Now  screw  up  the  stuffing  box  nut  (having  previously  removed 
the  packing),  then  move  the  valve  and  stem  so  that  the  small  port  at  right  of  valve  will  be 
open  one-sixteenth  inch  and  make  a  scratch  upon  the  stem  close  to  stuffing  box  nut.  The 
valve  should  then  be  moved  in  the  opposite  direction  to  open  the  other  small  port  one- 
sixteenth  inch  and  make  a  second  scratch  upon  the  valve  stem  next  to  stuffing  box  nut.  Pre- 
pare joint,  and  replace  steam  chest  on  cylinder.  To  square  the  valve,  slacken  the  screw  in 
cross  head  and  move  the  latter  to  the  end  of  stroke  with  edge  of  cross  head  flush  with  the 
end  of  guide,  then  set  the  valve  stem  so  that  the  first  scratch  is  flush  with  the  face  of  nut, 
same  as  when  the  scratch  was  made.  Tighten  screw  in  set  screw  under  valve  rod  dog  and 
move  the  cross  head  to  the  opposite  end  of  stroke,  and  note  the  position  of  second  scratch. 
If  it  do  not  come  to  the  position  in  which  it  was  made,  split  the  difference  by  slackening  the 
set  screw  under  valve  rod  dog  and  move  the  valve  rod  to  equalize  the  travel  of  valve.  In  replacing 
steam  chest  on  cylinder,  cover  the  opening  with  a  thin  board,  or  piece  of  sheet  iron,  before 
turning  it  over  to  prevent  the  valve  dropping  out  of  place. 


424 


PUMP  VALVE  GEARS 


^^^^^^^^^^^^^^^ 


fMi 


without  jar  or  noise  which  is  often  caused  by  long  travel 
steam  chest  at  B,  and  fills  the  space  F,  between 
auxihary  valve  chest  G,  shown  in  fig.  776.  With  the 
shown,  fig.  777,  steam   passes  into  both  ports  J  and 


Figs.  776  to  778.— Valve  gear  of 
the  fiurn/iam  pump.  Fig.  778 
is  a  plan  of  the  main  cylinder 
valve  face,  having  the  same 
arrangement  of  ports  as  the 
cylinder  shown  in  fig.  777.  A 
longitudinal  section  of  the 
steam  cylinder  is  shown  in  fig. 
776.  Motion  is  imparted  to  the 
slotted  arm  and  cam  A,  by 
means  of  a  cross  head  and  a 
roller  on  the  piston  rod.  The 
cam  work?  between  and  in 
contact  with  two  blocks  on  the 
valve  stem,  and  by  adjusting 
these  two  blocks  the  stroke 
may  be  shortened  or  lengthened 
as  the  case  may  require.  The 
valve  stem  of  the  auxiliary 
valve  H,  fig.  777,  always  moves 
in  a  direction  opposite  to  that 
of  the  piston.  The  action  of 
this  valve  alternately  admits 
steam  through  the  double  ports 
J  J  and  K  K,  to  each  end  of 
the  valve  cylinder,  causing  the 
valve  piston  I,  to  move  the 
main  slide  valve  D,  which,  in 
turn,  admits  steam  to  the  main 
cylinder  through  the  double 
ports  E  E  and  L  L.  As  the 
travel  of  the  cam  is  only  one- 
fifth  that  of  the  piston  traveU 
the  valve  moves  slowly,  and 
and  rapid  motion.  Steam  enters  the 
the  valve  piston  heads  and  the 
auxiliary  valve,  H,  in  the  position 
K,   but    as  the  port  Ji,  is  closed 


PUMP  VALVE  GEARS  425 


again  be  tried  under  steam,  and  the  ends  of  the  stroke  should  again  be 
marked. 

Should  the  marks  denoting  the  clearance  of  the  pistons  again  fall  on  the 
same  points  as  before,  and  a  difference  in  the  clearance  on  both  ends  of  the 
stroke  be  found,  the  trouble  will  be  due  to  the  irregular  spacing  of  the 
ports  in  the  cylinder  bore,  and  there  will  be  little  chance  for  improvement, 
and,  unless  the  cross  head  be  found  considerably  out  of  adjustment,  it 
should  not  be  disturbed,  and  the  final  valve  adjustment  should  be  made 
to  suit  the  extremes  of  the  stroke  while  running. 

It,  however,  rarely  occurs  that  a  pump  is  of  such  poor  workmanship 
as  to  make  proper  adjustment  impossible. 

The  location  of  the  ends  of  the  stroke  does  not  make  any  difference  in 
the  manner  of  adjusting  the  valve,  except,  that  it  must  be  noted  that  in 
one  case,  by  the  end  of  the  stroke,  the  extreme  positions  of  the  pistons 
when  pried  over,  and  in  the  other  case  the  end  positions  of  the  pistons  when 
allowed  to  run,  are  meant. 

How  to  Set  the  Valves  of  a  Duplex  Pump. — Place  a  small 
stick  or  batten  against  the  end  of  the  valve  chest,  and  mark  the 
center  of  the  pin  P  on  the  same,  as  indicated  in  fig.  762.  Then 
move  the  piston,  of  the  same  side,  to  the  other  end  of  the  stroke, 
and  again  mark  the  position  of  the  pin  P,  on  the  same  stick,  as 
indicated  by  the  dotted  lines.  The  two  marks  M,  and  N,  thus 
obtained,  denote  the  extreme  travel  of  the  pin  P. 

It  will  now  be  necessary  to  obtain  the  marks  X  and  Y  on  the  same  stick, 
which  indicate  the  positions  of  the  pin  L  when  the  valve  has  moved  from 
one  full  port  opening  to  the  other.  * 


Figs.  776  to  778. — Continued. 

by  the  valve  piston  I,  no  steam  can  enter  the  valve  cylinder  through  it,  but  the  other  port, 
K  (extending  to  the  extreme  end  of  the  valve  cylinder),  never  being  covered  by  the  piston, 
is  open,  and  admits  steam  into  the  space  M.  As  this  port  is  quite  small  the  space  fills  slowly 
and  the  piston  moves  gradually  until  it  uncovers  the  last  port  Ji,  when  the  full  volume  of 
steam  is  admitted,  which  quickly  moves  the  piston  to  the  opposite  end  of  the  valve  cylinder. 
During  this  movement  of  the  valve  piston,  the  large  port  J,  remains  open  to  the  exhaust 
until  it  is  covered  by  the  valve  piston.  When  the  port  J,  is  covered  by  the  valve  as  at  Ji, 
it  has  no  connection  with  the  exhaust,  consequently,  there  being  no  outlet  for  the  exhaust 
vapor,  it  is  compressed  and  forms  a  cushion  for  the  valve  piston,  I.  The  valve  piston  carries 
with  it  the  main  valve  D,  which  admits  steam  to  the  main  steam  cylinder  through  the 
double  ports  E,  Ei,  and  L,  Li,  fig.  776.  The  same  cushioning  and  slow  starting  of  the  piston 
occurs  in  the  main  as  in  the  valve  cylinder,  each  having  double  ports. 

To  set  the  valve. — Set  the  lever  A,  plumb  and  the  valve  to  cover  all  the  ports  equally. 


*N0TE. — ^When  sliding  the  valve  from  one  "full  port"  to  the  other,  care  should  be  taken 
to  do  this  by  moving  the  valve  stem,  to  obtain  the  full  effect  of  the  lost  motion  between  the 
nut  and  the  lugs  on  the  back  of  the  valve  as  in  fig.  760. 


426 


PUMP  VALVE  GEARS 


Now  take  a  strip  of  stiff  paper,  and  mark  upon  it  the  exact  distance 
between  the  center  of  the  holes  in  the  valve  connecting  link,  as  D  and  E, 
fig.  779.  Try  the  distance  between  the  marks  D  and  E,  on  the  strip  of  paper, 
against  the  marks  X  and  M,  and  Y  and  N,  and  if  they  should  coincide  as 
in  fig.  780,  the  valve  is  correctly  adjusted,  and  the  links  should  be  put  into 
their  places,  and  the  valve  chest  cover  replaced. 


^^ 


"TIT 


F 


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za 


IVI       N 


\^i'      u 

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1                             A           A 

A 

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M 

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i   ^i-              1   Nl/ 

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W 

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A 

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M    N 


^r 


M/ 


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TT 


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Figs.  779  to  784. — Paper  template  and  batten   with   center  marks  as  used  in  adjusting  the 
valves  of  a  duplex  pump  as  fully  explained  in  the  accompanying  text. 


PUMP  VALVE  GEARS 


427 


If,  however,  the  marks  should  fall  as  in  fig.  781,  or  fig.  782,  it  is  evident 
that  the  valve  stem  is  either  too  short  as  in  fig.  781,  or  too  long  as  in  fig.  782, 


STEAM  CHEST. 


Figs.  785  to  789. — Valve  gear  of  the  Warren  pump.  To  set  the  valve  gear:  1,  Move  piston 
valve  A,  and  steam  piston  B,  until  they  strike  the  heads  of  steam  chest«and  steam  cylinder, 
fig.  785.  2,  Place  clamp  D,  so  as  to  allow  J^  inch  for.Nos.  1,  2,  3,  4;  %  inch  for  Nos. 
5,  6.  6^;  1  inch  for  Nos.  7, 8, 9,  10,  U,  12, 13,  five  port;  M  inch  for  Nos.  7,  8, 9, 10, 11, 12, 13, 
three  port,  between  clamp  and  tappet  arm  G,  fig.  785,  also  between  tip  and  collar  E,  fig.  787. 
3,  Set  clamp  D,  so  that  as  you  roll  or  turn  the  valve  rod  in  either  direction  as  far  as  it  will 
go,  the  clamp  will  be  equally  above  and  below  the  level.  4,  Even  up  the  motion  of  rocker  R, 
by  screwing  the  upper  part  of  rocker  connection  L,  out  or  in  as  required.  5,  Set  the  roll  K. 
in  tappet  arm  I,  up  or  down,  so  as  to  allow  ^/fg  inch  between  rocker  and  roll,  when  the  latter 
is  at  its  extreme  of  travel.  Note  the  little  set  screw  S,  in  roll  stud  T,  fig.  789,  which  is  adjustable 
to  rest  on  bottom  of  tappet  arm  slot,  and  prevent  the  roll  stud  working  down  after  it  has 
been  set  in  its  proper  position.  6,  If,  when  the  pump  is  run  under  steam,  the  tip  G,  strike 
clamp  or  collar  violently  before  reversing  its  motion,  the  tappet  arm  roll  K,  needs  to  be  raised, 
a  little  at  a  time,  until  such  action  ceases,  otherwise  the  tip  is  liable  to  be  broken.  If,  on 
the  other  hand,  the  pump  run  short  stroke,  drop  the  roll.  The  best  adjustment  is  when  the 
tip  just  misses  hitting  clamp  and  collar,  when  the  pump  is  doing  its  regular  work. 


428 


PUMP  VALVE  GEARS 


and  it  must  be  either  lengthened  an  amount  equal  to  the  distance  E  Y, 
fig.  781,  or  shortened  an  amount  equal  to  the  distance  E  Y,  in  fig.  782. 

Figs.  783  and  784,  show  other  positions  in  which  the  marks  on  the  stick 
and  the  strip,  of  paper  may  fall.  In  both  cases,  the  travel  of  the  valve 
between  the  two  inside  edges  of  the  steam  ports  evidently  does  not  coincide 
with  the  travel  of  the  pin  P,  fig.  762,  indicating  that  there  is  either  too 
much  lost  motion  between  the  valve  stem  and  the  valve,  as  in  fig.  783, 
or  not  sufficient,  as  in  fig.  784.  Before  attempting  to  alter  this,  it  is  advisable 
to  remove  the  valve  entirely,  and  to  see  whether  the  distance  between  the 
steam  and  exhaust  edges  of  the  valve,  as  F  and  G,  and  H  and  I,  fig.  760, 
correspond  with  the  distances  between  the  working  edges  of  the  ports 


Fig,  790. — ^Rocker  arm  and  connections  as  usually  designed  for  large  pumps,  with  lost  motion 
adjustment.  In  this  arrangement,  the  lost  motion  can  be  adjusted  while  the  pump  is  in 
operation. 


K  and  O,  and  Q  and  R,  respectively  (fig.  761).  If  these  distances  agree 
with  each  other,  and  the  marks  representing  the  valve  and  pin  travel  fall  as 
in  fig.  783,  it  indicates  that  the  valve  has  not  sufficient  motion  to  fully  open 
the  ports,  hence  less  lost  motion  has  to  be  given.  Fig.  784  shows  the  re- 
verse of  this  condition. 

Should  the  distance,  between  the  edges  F  and  G,  or  H  and  I,  be  found 
shorter  than  the  distance  between  their  respective  port  edges,  an  amount 
equal  to  one-half  the  difference  between  E'  E  and  X  Y,  fig.  784,  the  steam 


PUMP  VALVE  GEARS 


429 


edge  of  the  valve  will  over  travel  the  inner  edge  of  the  steam  port,  when  the 
valve  is  connected  up,  but  the  exhaust  port  would  have  just  full  openings 
indicating  that  there  is  some  exhaust  lap,  and  if  the  pump  be  found  to  run 
smooth,  it  is  advisable  not  to  tamper  with  the  adjustment  of  the  lost 
motion. 

If  it  be  necessary  to  increase  the  lost  motion  between  valve  and  stem, 
on  a  pump  provided  with  such  an  adjustment  as  in  fig.  762,  it  can  be 
done  by  decreasing  the  width  of  the  nut,  by  filing  or  machining  in  a  shaper. 

To  decrease  the  lost  motion,  either  a  new  nut  must  be  provided,  or  sheet 
metal  washers  of  the  required  thickness  may  be  cut,  and  placed  on  the  valve 
stem  between  the  nut  and  the  lugs  on  the  back  of  the  valve. 

The  method  of  valve  setting  just  described  is  only  suitable  for  small 
pumps;    the  larger  ones  generally  being  provided  with  an  adjustment  as 


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U           M    1                       ilili'l 

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L-O— J 

N 

"""^ 

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^ 

Fig.  791. — Lost  motion  arrangement  consisting  of  yoke  M,  and  block  S,  pivoted  at  the  rocker 
end.  In  this  design  the  lost  motion  cannot  be  changed  without  altering  the  length  of  the 
block  S,  but  the  length  of  the  valve  stem  can  be  adjusted  by  means  of  the  sleeve  nut  N. 


in  figs.  760,  761  and  791.  The  arrangement  shown  in  figs.  760  and  761, 
is  very  simple,  and  permits  accurate  adjustment,  but  in  order  to  do  this,  it  is 
necessary  to  remove  the  valve  chest  cover. 

The  type  shown  in  fig.  791,  is  mostly  used  on  large  and  more  expensive 
pumps,  and  permits  alterations  in  the  adjustment  being  made  while  the 
pump  is  running. 

In  fig.  791,  the  lost  motion  can  not  be  altered,  without  taking  off  or  adding 
to  the  ends  of  the  block  S,  but  the  sleeve  nut  in  the  connecting  link  is  a 
good  device  for  altering  the  length  of  the  valve  stem. 

It  is  seldom  the  case  that  the  amount  of  lost  motion  has  to  be  alter- 
ed, and  unless  the  operator  be  thoroughly  familiar  with  the  details 
and  design  of  the  pump,  he  should  not  undertake  such  alterations,  as 
the  designer  knows  best  what  the  requirements  are. 


430 


PUMP  VALVE  GEARS 


The  above  directions  can  not  always  be  closely  followed,  as  the  different 
designs  require  different  treatment,  but  by  thoroughly  understanding  the 
above,  the  beginner  will  be  greatly  assisted  even  with  the  most  com- 
plicated construction. 

Short  Rules  for  Setting  the  Valves  of  a  Duplex  Pump. — 

It  maybe  helpful  in  acquiring  a  knowledge  of  how  to  set  the  valves 


Fig.  792. — Sectional  view  of  A  merican  deep  well  pumping  head  showing  valve.  In  the  position 
shown  the  steam  is  passing  through  ports  1,  2,  3,  4,  and  choke  valve  5,  into  the  cylinder  7. 
Piston  rod  6,  is  connected  to  the  pumping  rods  that  extend  down  into  the  well  to  the  water 
plunger.  The  number  of  strokes  is  regulated  by  the  choke  valves  5,  16  and  17.  Port  8,  is 
opened  for  the  exhaust  of  steam  out  through  9.  Just  before  the  piston  10,  reaches  the  end 
of  its  stroke,  it  closes  the  exhaust  port  8,  and  forms  a  cushion.  At  the  same  time  the  valve 
stem  11,  is  also  turned  by  a  roller  on  the  cross  head,  striking  a  finger  cam  on  the  valve  stem. 
The  movement  changes  the  position  of  the  auxiliary  valve  12.  Steam  will  then  flow  through 
suitable  ports  and  will  move  the  valve  13,  so  that  port  14,  is  uncovered,  allowing  stearn  to 
enter  the  upper  end  of  the  cylinder  and  cause  the  piston  to  move  in  the  reverse  direction. 
At  the  same  time  port  15,  is  brought  into  communication  with  exhaust  9.  Choke  valve  16, 
controls  the  exhaust  and  helps  the  regulation  of  the  pump.  In  operating  a  single  acting 
cylinder,  where  the  weight  of  pump  rods  is  heavier  than  water,  no  steam  is  used  on  the  down 
stroke;  then  valve  17,  is  closed  and  valve  16,  shut  sufficiently  to  sustain  the  weight  of  the 
pump  rods  and  give  the  required  number  of  strokes.  When  the  double  acting  and  two  stroke 
cylinders  are  used,  valve  17  is  opened  sufficiently  to  give  a  uniformity  to  up  and  down  strokes. 


PUMP  VALVE  GEARS 


431 


to  consider  simply  the  essential  operations  without  the  various 
details  or  methods  of  performing  them  as  given  in  the  foregoing 
instructions :  They  may  be  briefly  expressed  in  the  form  of  rules 
as  follows : 

1.  Locate  ike  steam  piston  in  the  center  of  the  cylinder; 


Fig.  793. — ^Valve  gear  of  the  McGowan  pump.  Its  main  valve  is  of  the  B  form  and  is  driven 
by  a  valve  piston.  Steam  enters  the  central  port  in  valve  seat  and  into  the  cylinder  through 
one  of  the  cavities  in  the  valve  and  exhausts  through  the  opposite.  The  two  tappet  valves 
cover  the  auxiliary  ports,  shown  by  dotted  lines,  leading  to  the  ends  of  the  steam  chest  and 
connect  with  the  main  exhaust  ports.  When  the  piston  reaches  the  end  of  its  stroke  it  lifts 
one  of  the  tappet  levers  and  with  it  the  corresponding  valve  is  raised  from  its  seat,  opening 
the  port  leading  from  the  end  of  the  steam  chest  to  the  main  exhaust  port.  The  pressure  is 
thus  relieved  on  one  end  of  the  valve  piston  and  the  steam  pressmg  on  the  opposite  end 
forces  the  valve  piston  to  the  opposite  end  of  its  stroke,  thus  reversing  the  distribution  of 
steam  to  the  cylinder  and  starting  the  piston  on  its  return  stroke.  The  main  valve  is  con- 
nected with  the  valve  piston  so  that  all  lost  motion  is  taken  up  automatically.  A  rocker 
shaft,  extending  through  the  steam  chest  carries  a  toe  moving  in  a  slot  in  the  top  of  the  valve 
piston,  so  that  the  valve  can  be  moved  by  hand. 

To  set  the  valves. — Simply  keep  the  valves  in  order.    The  motion  of  the  piston  as  it 
nears  the  end  of  the  stroke  opens  and  closes  the  valves. 


432  PUMP  VALVE  GEARS 


This  is  accomplished  by  pushing  the  piston  to  one  end  of  its  stroke 
against  the  cyhnder  head  and  marking  the  rod  with  a  scriber  at  the  face 
of  the  stuffing  box,  and  then  bringing  the  piston  in  contact  with  the  opposite 
head. 


2.  Divide  exactly  the  length  of  this  contact  stroke; 


Shove  the  piston  back  to  this  half  mark;  which  brings  the  piston  directly 
in  the  center  of  the  steam  cylinder; 


3.  Perform  the  same  operation  with  the  other  side; 

A,  Place  the  slide  valves  in  their  central  position; 

5.  Pass  each  valve  stem  through  the  stuffing  box  and  gland; 


The  operation  of  placing  the  pistons  in  the  center  of  their  cylinders  brings 
the  levers  and  rock  shafts  in  a  vertical  position ; 


6.  Screu)  the  valve  stem  through  the  nuts; 


The  stem  is  screwed  until  the  hole  in  the  eye  of  the  valve  stemi  head  comes 
in  a  line  with  the  hole  in  the  links,  connecting  the  rocker  shaft. 


7.  Put  the  pins  in  their  places; 

8.  Adjust  the  nuts  on  both  sides  of  the  lugs. 

Leave  about  one-eighth  to  one-fourth  inch  lost  motion  on  each  side. 


VALVE  SETTING 


433 


CHAPTER    13 
VALVE   SETTING 


How  to  Set  the  Slide  Valve. — In  tlie  ordinary  valve  gear, 
such  as  the   type   shown  in   fig.   794,   the  eccentric  is  retained 

in  position  on  the  shaft  by  a  set 
screw,  and  the  length  of  the  valve 
stem  made  adjustable  by  a  thread- 
ed end  with  jamb  nut,  or  equiva- 
lent. The  valve  stem  may,  there- 
fore, be  lengthened  or  shortened, 
and  the  eccentric  placed  in  any 
angular  position. 

On  assembling  the  valve  gear  it 
is  found  that  the  dimensions  for  the 
valve  stem  length,  and  eccentric  posi- 
tion are  lacking. 

In  setting  the  valve  there  are 
three  distinct  operations  which  are 
to  be  performed  in  the  order  here 
given: 

1 .  Locating  the  engine  on  the  dead 
centers; 

2.  Finding  the  length  of  the  valve 
stem,  that  is,  equalizing  the  lead; 

"^  witrorTini'^"  v^^fve  "gtr^  atSe  3.  Determining  the  correct  position 

?LTrfV\wTset?fng"'^'  '°^  ^^^"         of  the  ecccntric. 


434  VALVE  SETTING 


How  to  Find  the  Dead  Center. — The  engine  is  located  on 
the  dead  center  with  a  tram,  such  as  shown  in  fig.  795. 

This  consists  of  a  piece  of  one-fourth  inch  or  three-eighth  inch  tool  stee! 
rod,  of  suitable  length  corresponding  to  the  size  of  the  engine  and  having 
a  small  portion  at  one  end  bent  to  a  right  angle;  each  end  being  ground 
to  a  fine  point  and  hardened.  The  tram,  in  fact,  corresponds  to  the  bent 
scriber  of  a  scribing  block. 

A  permanent  center  punch  mark  is  made  on  the  engine 
frame  to  receive  the  straight  end  of  the  tram,  and  a  ring  of  small 
punch  marks  made  around  this  permanent  mark,  to  easily 
identify  its  position  for  future  occasions,  especially  after  painting. 


Fig.  795. — Tram,  or  instrument  used  in  finding  the  dead  center  of  an  engine.     It  corresponds 
to  the  bent  scriber  of  a  machinist's  scribing  block. 

On  a  vertical  engine,  the  permanent  mark  may  be  located  on  the  column 
or  bed  plate;  on  a  horizontal  engine,  on  the  bed  plate,  in  either  case  the 
punch  mark  should  be  made  at  some  convenient  place  where  the  other 
end  will  reach  to  the  crank  disc,  or  fly  wheel. 


The  dead  center  may  now  be  located  as  follows:  The  engine 
is  .turned  in  the  direction  in  which  it  is  to  run  until  the  piston  has 
nearly  completed  the  stroke,  as  shown  in  fig.  796,  crank  position 
B.  A  mark  M,  to  indicate  this  position,  is  made  across  the 
guide  and  cross  head.  With  the  straight  end  of  the  tram  in 
the  permanent  punch  mark  P,  as  a  center,  an  arc  C,  is  described 
on  the  side  of  the  fly  wheel  rim,  the  surface  first  being  cleaned 
of  oil,  and  rubbed  with  chalk  so  the  mark  is  easily  seen.  The 
engine  is  now  turned  past  the  dead  center  until  the  mark  on 
the  guide  again  registers  with  the  mark  on  the  cross  head  cor- 
]"esponding  to  crank  position  A.     Arc  D,  is  now  described  with 


VALVE  SETTING 


435 


the  same  center  P,  and  an  arc  passing  through  C  and  D,  is 
described  from  the  center  of  the  shaft.  That  portion  of  the  arc 
included  between  C  and  D,  is  bisected,  giving  the  point  E.  A 
punch  mark  is  made  at  this  point  and  the  engine  turned  in  the 
direction  oj  its  future  rotation  until  E,  registers  with  the  bent 
end  of  the  tram  when  its  other  end  is  in  P.  In  this  position  the 
engine  is  on  the  dead  center.  The  other  dead  center  is  found 
in  a  similar  manner. 


Li  )                M        U 

Fig.  796.-7-Locating  the  engine  on  the  dead  center.  In  doing  this  as  described  in  the  text, 
the  engine  should  always  be  turned  in  the  direction  in  which  it  is  to  run  so  as  not  to  introduce 
any  error  due  to  lost  motion.  The  tram  marks  should  be  made  permanent  with  a  center 
punch. 

The  engine  should  always  be  turned  in  one  direction  in  order 
not  to  introduce  any  error  due  to  lost  motion  in  the  wrist  and 
crank  pins.  It  matters  not  which  direction  is  followed,  the 
object  being  to  have  the  crank  pin  pressing  against  the  same 
brass  for  each  adjustment.  It  is  usual,  however,  to  turn  the 
engine  in  the  direction  in  which  it  is  to  run,  presumably  because 
this  is  more  easily  remembered. 

In  case  the  engine  has  been  moved  too  far  at  any  time,  it  is 
not  necessary  to  complete  the  revolution,  but  merely  to  turn  it 
back  beyond  the  desired  point,  and  then  forward  again  up  to 
that  point  in  the  direction  of  rotation  thus  taking  up  the  lost 
motion  each  time  in  the  same  direction. 


436 


VALVE  SETTING 


Adjusting  the  Valve  Stem. — Having  located  the  dead 
centers,  the  second  step  is  to  equalize  the  lead,  that  is,  to  make  it 
the  same  at  each  end  of  the  cylinder.  First,  the  eccentric  is 
located  *'by  eye,"  placing  it  ahead  of  its  correct  position  rather 
than  behind. 


POSITIVE    LEAD 
EASILY     MEASURED 


NEGATIVE   LEAD 
HARD    TO    MEASURE 


V/////////77777Z. 


V//////A     vzzzz. 


Figs.  797  and  798. — Positive  and  negative  lead.  In  setting  a  valve  the  eccentric  is  first  located 
"by  eye."  The  figures  show  why  it  should  be  placed  ahead  of  its  correct  position  rather 
than  behind. 

With  the  eccentric  set  ahead,  the  lead  is  positive  at  each  end;  when 
behind,  it  will  probably  be  negative  at  one  or  both  ends,  that  is,  the  two 
lead  positions  of  the  valve  would  be  about  as  shown  in  figs.  797  and  798. 
The  reason  for  setting  the  eccentric  ahead  is  to  avoid  negative  lead  as  in 
fig.  798,  because  it  is  not  easily  measured. 

A  long  wooden  wedge  should  now  be  provided,  tapering  from  one-half 
inch  (more  or  less  depending  on  the  size  of  the  engine)  down  to  "nothing,'* 
and  cut  into  several  pieces  as  shown  in  figs.  799  to  801. 


Figs.  799  to  801.; — ^Wedges  for  measuring  lead.  Prepared  from  a  long  piece  of  wood,  tapered 
from  one-half  inch  (more  or  less  depending  on  the  size  of  the  engine)  down  to  "nothing" 
and  cut  in  several  pieces. 


With  eccentric  set  well  advanced,  the  engine  is  placed  on  the 
dead  center,  and  the  amount  of  lead  measured  by  one  of  these 
wooden  wedges,  after  which  the  lead  for  the  other  end  is  found 
in  a  similar  manner. 


VALVE  SETTING 


437 


In  measuring  the  leads,  a  suitable 
wedge  is  inserted  into  the  ports  as  far 
as  it  will  go,  as  shown  in  figs.  802  and 
803,  being  careful  to  keep  one  side  of 
the  wedge  in  contact,  that  is,  parallel 
with  the  end  of  the  valve,  and  per- 
pendicular to  the  seat.  For  each  end, 
a  line  is  scribed  across  the  wedge 
along  the  steam  edge  of  the  port,  as 
shown  in  the  figures;  these  lines  (A 
and  B,  fig.  804)  indicate  the  lead  at 
the  two  ends,  being  located  at  points 
on  the  wedge  where  the  thickness  is 
equal  to  first  and  second  leads.  A 
line  C,  drawn  half-way  between  A 
and  B  will  represent  the  average^ 
or  equalized  lead.  In  taking  lead 
measurements  with  a  wedge  the  same 
side  should,  of  course,  always  be 
placed  next  to  'the  valve. 


The  lead  may  now  be  equal- 
ized by  adjusting  the  length  of 
the  valve  stem  so  that  the  wedge 
will  enter  the  port  up  to  the  line 
of  average  lead  (C,  fig.  804).  If 
the  work  has  been  correctly  done, 
the  lead  will  be  the  same  at 
each  end. 

Finding  the  Correct  Posi- 
tion of  the  Eccentric. — Since 
the  eccentric  was  set  ''by  eye," 
the  lead  is  probably  too  great, 
or  too  small  as  the  case  may  be. 
To  correct  this,  the  eccentric  is 
turned  on  the  shaft,  in  the  di- 
rection in  which  the  engine  is  to 
run,    until    the   valve    has   the 


438 


VALVE  SETTING 


desired  lead.*  The  results  should  be  verified  by  testing  the  lead 
at  the  other  end,  and  if  both  leads  be  the  same,  the  valve  has 
been  correctly  set.f 

Finding  the  Correct  Position  of  the  Eccentric  on  Large 
Engines. — To  avoid  the  frequent  turning  of  the  engine  from 
one  dead  center  to  the  other,  the  necessary  adjustments  may 
be  made  by  equalizing  the  port  opening  instead  of  the  lead. 
The  eccentric  is  turned  until  it  gives  the  maximum  port  opening, 


Fig.  804.— Equalizing  the  lead.  After  obtaining  the  lead  lines  A  and  B,  as  in  figs.  802  and  803,  a 
line  C,  is  scribed  half  way  between,  which  gives  the  average  lead.  The  valve  stem  is  then 
adjusted  so  that  the  wedge  will  enter  the  port  up  to  C,  thus  making  the  lead  the  same  at 
each  end  of  the  cylinder. 


first  at  one  end,  and  then  at  the  other.  These  port  openings, 
if  unequal,  are  equalized  by  adjusting  the  length  of  the  valve 
stem,  after  which,  the  engine  is  placed  on  the  dead  center,  and 
the  eccentric  turned  until  the  valve  gives  the  desired  lead. 


*NOTE. — The  lead  given  to  engines  varies  considerably  from  a  small  negative  lead  to 
three-eighths  inch  or  more  positive  lead,  depending  on  the  type  and  size  of  the  engine;  its 
amount  is  decided  upon  arbitrarily  by  the  designer  but  may  be  varied  in  setting  the  valve 
simply  by  changing  the  angular  advance  of  the  eccentric.  In  general,  the  amount  of  lead 
depends  on  the  speed  of  rotation,  and  the  inertia  of  the  reciprocating  parts. 

tNOTE. — In  order  to  clearly  fix  in  mind  the  general  principles  involved  in  setting  a  slide 
valve,  it  is  recommended  that  the  instructions  be  read  a  second  time,  omitting  the  minor 
details  given  in  the  small  type,  as  these  tend  to  divert  the  attention  from  the  important 
operations. 


VALVE  SETTING 


439 


Setting  the  Slide  Valve  Without  Removing  the  Steam 
Chest  Cover. — If  the  set  screw  of  the  eccentric  should  work 
loose  during  operation,  and  the  eccentric  change  its  position, 
it  may  be  quickly  reset  without  taking  off  the  steam  chest  cover, 
thus  saving  valuable  time  in  case  of  a  shut  down. 


A  permanent  punch  mark  is  made  on  the  end  of  the  steam  chest  as  at 
A,  fig.  805,  for  taking  measurements  on  the  valve  stem  with  a  tram.    The 


EXTREME    r05ITI0NS 


^J^_^=S^I    LEAD   POSITIONS 


Figs.  805  and  806. — Method  of  setting  the  valve  without  removing  the  steam  chest  coyer, 
when  the  valve  stem  does  not  require  adjustment.  It  consists  in  equalizing  the  two  positions 
L,  L',  of  the  valve  when  the  engine  is  on  the  corresponding  dead  center. 


eccentric  is  fastened  in  any  position,  and  the  engine  turned  until  the  valve 
is  at  one  end  of  its  travel.  A  tram  mark  B ,  is  made  on  the  stem  to  indicate 
this  position,  and  similarly  another  mark  C,  to  indicate  the  other  end  of  the 
valve  travel.  The  engine  is  placed  on  each  dead  center  and  the  position 
of  the  valve  located  by  the  tram.  This  gives  the  two  linear  advance 
positions  L  and  L',  of  the  valve,  which  in  case  the  eccentric  has  been  in- 
correctly set,  are  at  unequal  distances  L  B  and  L'C,  from  B  and  C. 

It  remains  to  adjust  the  position  of  the  eccentric  until  L  B,  is  equal  to 
L'  C,  as  shown  in  fig.  806.  With  this  condition  fulfilled,  the  valve  is 
correctly  set. 


440 


VALVE  SETTING 


Setting  the  Slide  Valve  Without  Finding  the  Dead 
Centers. — In  the  case  of  a  very  large  engine  where  the  operation 
of  putting  the  engine  on  the  dead  centers  would  require  one  or 
more  assistants,  the  following  method  will  be  found  useful. 
It  consists  of: 

1.  Equalizing  the  port  opening; 

2.  Finding  the  angular  advance. 


TOO  SMALL 


CENTER  OF 
ECCENTRIC 


Figs.  807  and  808. — Setting  the  valve  without  putting  engine  on  the  dead  center:  1,  equalizing 
the  port  opening. 


Equalizing  the  Port  Opening. — For  this  purpose  a  pair 
of  inside  calipers  may  be  used  when  the  port  opening  exceeds 
the  width  of  the  port,  or  if  less,  a  wedge  should  be  used. 


VALVE  SETTING 


441 


Loosen  the  eccentric  and 
turn  it  until  the  valve  is  at 
one  end  L,  of  its  travel  and 
measure  the  port  opening  as 
in  fig.  807.  Mark  this  distance 
for  reference  with  aid  of  a 
scriber  as  A,  in  fig.  809. 

Similarly  determining  the  port 
opening  at  the  other  end  when 
the  valve  is  at  that  end  F,  of  its  \ni 
travel  as  in  fig.  808,  and  mark  it 
as  B ,  in  fig.  809.  If  unequal,  set 
calipers  for  average  port  opening 
C,  in  fig.  809. 

Now  rotate  eccentric  until  valve 
is  at  either  end  of  its  travel  and 
adjust   length  of  valve  stem  till 
valve  gives  the  average  port 
opening  according  to  average 
setting  C,  of  calipers. 


Fig.  809. — Method  of 
finding  average  port 
opening  with  inside 
calipers  and  scriber. 
After  setting  cali- 
pers for  port  open- 
ing A,  fig.  807,  draw 
alineasMS.fig.  809 
and  place  ends  of 
caliper  legs  on  this 
line ;  mark  these 
points  aa\  with  scri- 
ber as  shown.  Sim- 
ilarly, set  calipers  for 
port  opening  B ,  fig. 
808,  and  transfer  to 
MS,  fig.  809,  meas- 
uring from  a,  and 
obtaining  point  h. 
Bisect  a'b,  by  de- 
scribing arcs  about 
a\  and  b,  as  centers, 
obtaining  the  point 
c,  at  foot  of  a  per- 
pendicular through 
the  intersection  of 
the  arcs,  ac,  or  C, 
then  is  the  average 
port  opening  for 
which  the  calipers 
*nust  be  set.  The 
wedge  method  as 
was  used  for  equal- 
izing the  lead 
can  be  used 
\  j^  Q  to  advantage 
i  O  when  the  port 
I  opening  is 

I  less  than  the 

width  of  the 
port. 


\>v 


^SETTING 

Compare  port  open- 
ing at  other  end  and  if 
the  work  has  been  ac- 
curately done,  both  port  open- 
ings will  be  the  same,  that  is^ 
the  port  opening  has  been 
equalized,  as  in  figs.  810  and 
811. 


Finding  the  Angular 
Advance . — The    several 
operations  to  be  performed 
in  finding  the  angular  advance 
and    placing   tne  eccentric   in   angular   advance    position   are: 


442 


VALVE  SETTING 


1.  Rotating  eccentric  till 
valve  is  in  lead  position; 

2.  Finding  angular  ad- 
vance ; 

3.  Transferring  angular 
advance  to  reference  mark 
on  shaft; 

4.  Rotating  eccentric  to 
angular  advance  positi'bn. 

Performing  these  operations 
in  the  order  given,  first  rotate 
eccentric  until  the  valve  has 
the  desired  lead  and  locate 
this  position  of  the  eccentric 
by  scribing  a  line  M,  on  the 
eccentric  and  L,  on  the  shaft 
as  in  fig.  812. 

Now  measure  diameter  of 
shaft  at  eccentric  with  outside 
calipers  and  set  dividers  to 
half  this  length.  Wipe  all 
grease  from  the  crank  and 
chalk  same.  With  one  end  of 
the  dividers  in  the  lathe  center 
scribe  a  circle  R,  correspond- 
ing to  the  shaft  diameter  as 
in  fig.  813. 

Next  take  a  small  string,  or 
preferably  strong  flax  thread 
and  make  a  loop  at  one  end 
and  place  it  around  the  crank 
pin ;  pull  very  taut,  holding  it 
so  that  it  intersects  the  shaft 
lathe  center,  and  scribe  the 
point  F',  where  it  cuts  the 
shaft  circle.  The  thread  then 
represents  the  center  line  of 
the  crank. 

Now  by  means  of  a  level, 
scribe  a  horizontal  line  passing 
through  the  shaft  center  and 
cutting  the  shaft  circle  at  L, 
Evidently  the  angle  LAF,  is 
the  angular  advance^  which  can 
be  easily  transferred  to  the 
eccentric  by  a  pair  of  dividers. 


VALVE  SETTING 


443 


O  O  »fc  O  O  J>>  ,TM  0) 

<0    O    O    grd-S    O       ..S 

:2  o  ..  «  §  J  ^^-^ 


o-d  C  ?^  5i 


cJ  s.  <-"  -* 


444 


VALVE  SETTING 


^^z^z^:^^ 


l.l.lfi.l.iJil.i.i.lfi.LiL 


Figs.  815  to  817. — Setting  an.  inside  admission  piston  valve.  The  two  extreme  positions 
are  measured  as  in  tig.  815,  and  the  travel  equalized  by  adjusting  the  valve  stem.  The 
engine  is  placed  on  each  dead  center,  and  measurements  taken  as  in  figs.  816  and  817.  The 
position  of  the  eccentric  is  then  adjusted  until  E,  fig.  816,  equals  E',  fig.  817.  If  M  and  S  be 
unequal  due  allowance  should  be  made. 


VALVE  SETTING  445 


Set  the  dividers  as  in  fig.  813  to  measure  the  arc  M'  S,  then  place  one  leg 
of  the  dividers  on  M,  in  fig.  812  and  lay  off  M  S,  in  the  direction  of  rotating. 

Turn  the  eccentric  till  its  reference  mark  M,  coincides  with  S,  as  in  fig. 
814  and  secure  eccentric  in  this  position,  when,  if  all  the  operations  have 
been  properly  performed  the  setting  will  be  found  correct. 

Setting  an  Inside  Admission  Piston  Valve. — In  this  type 
of  valve  the  steam  edge  of  the  port  being  on  the  inside,  the 
valve  cannot  be  set  by  direct  lead  measurements  as  with  the 
slide  valve;  use  is  therefore  made  of  the  exhaust  edge  of  the 
valve  as  a  basis  for  measurements.  The  necessary  operations 
in  setting  the  valve  should  present  no  difficulty  if  the  two 
following  principles  be  understood  and  remembered: 

1.  The  two  extreme  positions  of  the  valve  must  be  equally  distant 
on  either  side  of  the  neutral  position. 

2.  With  equal  lead,  the  linear  advance  must  he  the  same  for  each 
end  of  the  cylinder , 

Applying  the  first  principle ^  the  valve  gear  is  adjusted  so  that 
the  valve  travels  an  equal  distance  each  side  of  its  neutral 
position. 

To  do  this,  the  eccentric  is  set  in  any  position  on  the  shaft,  and  the 
engine  turned  over  until  the  valve  has  reached  one  end  of  its  travel  as 
position  A,  fig.  815.  The  distance  E,  from  the  exhaust  edge  of  the  valve 
to  the  end  of  the  cylinder,  is  measured,  and  similarly,  distance  E'  when  the 
valve  is  at  the  other  end  of  its  travel,  as  in  position  B,  shown  in  dotted 
lines.  If  the  length  of  the  valve  stem  be  not  correct,  these  two  distances 
will  be  unequal.  The  travel  is  now  equalized  by  adjusting  the  length 
of  the  valve  stem  until  these  distances  become  equal,  that  is,  until  E=E'. 

Applying  the  second  principle,  the  engine  is  placed  on  each 
dead  center,  and  the  distances  of  the  exhaust  edges  of  the  valve 
from  the  ends  of  the  cylinder  measured. 

If  the  eccentric  has  not  the  proper  angular  advance,  these  distances 
will  be  unequal,  and  it  remains  to  adjust  the  position  of  the  eccentric  until 
they  become  the  same,  a?  shown  in  figs,  416  and  417, 


446 


VALVE  SETTING 


When  E,  fig.  816  is  equal  to  E'  fig.  817  the  linear  advance 
is  the  same  for  each  end  of  the  cylinder,  hence  the  lead  has  been 
equalized  and  the  valve  correctly  set. 

Before  setting  an  inside  admission  valve  as  just  outlined,  the  location 
of  the  ports  with  respect  to  the  cylinder  ends  should  be  carefully  determined. 
In  most  cases  these  are  equidistant  from  the  ends,  that  is,  M  =  S,  fig.  818; 
if  not,  due  allowance  should  be  made  in  setting  the  valve. 

In  locating  the  ports,  the  measurements  are  conveniently  made  with 
an  ordinary  rule  having  a  strip  of  metal  soldered  on  the  brass  end  as 


EXHAUST  EDGE 


L 


J3IIEZIJ 


coaziisEi 


Fig.  818. — Method  of  measuring  the  location  of  the  ports.  ^  A  strip  of  metal  is  soldered  on  the 
brass  end  of  the  scale  as  shown,  being  placed  at  the  side  to  measure  the  steam  edge  M, 
and  over  the  end,  for  the  exhaust  edge  S. 

shown  in  fig.  818;  in  setting  the  valve,  a  short  steel  rule  is  used.  In  either 
case  a  square  or  straight  edge  is  used  in  taking  the  readings  to  project  the 
plane  of  the  cylinder  to  the  rule  as  shown  in  the  figures.  The  rule  must 
be  held  plumb  with  the  valve  to  avoid  error. 


Emergency  Rule  for  Setting   the  Slide  Valve. — If  the 

eccentric  should  slip  on  the  shaft,  or  any  other  accident  throw 
the  valve  gear  out  of  position,  it  may  be  quickly  reset  as  follows: 
The  engine  is  placed  on  the  dead  center  and  the  eccentric  turned 
a  little  behind  its  correct  position. 

With  the  cylinder  drain  cocks  open,  a  small  amount  of  steam 


VALVE  SETTING 


447 


0) 

o 

rCl 

^j 

•4-> 

C/3 
U 

CD 

o 

a 

^ 

9^ 

448 


VALVE  SETTING 


Taking  Laths  from  the  Valve  and  Seat. — It  is  desirable 
to  have  permanent  records  of  the  valve  and  seat  dimensions, 
which  are  useful  in  setting  the  valve.  These  dimensions  are 
transferred  directly  to  laths  or  battens  made  of  wood,  and 
.SCRIBER 


Figs.  820  and  821. — Preparing  valve  and  seat  laths.    Care  should  be  taken  to  place  the  laths 
square  with  the  valve,  or  seat  as  indicated  by  use  of  the  try  square. 


planed  true  and  square;  they  should  measure  some  three  inches 
in  width  by  five-eighths  inch  thick  and  of  convenient  length, 
depending  on  the  size  of  the  engine. 

The  valve  is  removed  from  the  engine,  and  its  steam  and  exhaust  edges 
scribed  on  a  lath  as  shown  in  fig.  820,  care  being  taken  to  have  the  lath 


VALVE  SETTING 


449 


at  right  angles  with  the  edges.  Similarly  the  seat  dimensions  are  trans- 
ferred to  a  second  lath  as  shown  in  fig.  821.  The  spaces  on  the  laths 
representing  the  ports  and  exhaust  cavity  are  painted  white,  and  the  valve 
faces  and  bridges  black;  the  seat  batten  being  painted  black  at  the  ends 
between  the  ports  and  the  seat  limits.  The  ends  of  the  battens  should  be 
marked  H  and  C,  denoting  ''head  end"  and  "crank  end;"  the  completed 
battens  appearing  as  in  figs.  822  and  823. 

5L\DE  VALVE 


i^mm 


^SEAT   LIMIT       ^2.  TRAVEL 


Fig.  822  and  823. — Slide  valve  battens.  The  ports  and  exhaust  cavity  are  painted  white, 
and  the  valve  faces  and  bridges  black.  Lines  are  drawn  corresponding  to  the  half  travel,  or 
extreme  positions,  and  the  ends  marked  to  distinguish  head  and  crank  end. 

The  batten   is   specially  useful   with   engines   having  inside 
admission  piston  valves  as  a  check  on  the  valve  setting. 

The  cylinder  ends  as  well  as  the  bushings,  or  valve  seat  should  be  painted 
on  the  batten  as,  in  setting  the  valve,  measurements  are  taken  from  the 
ends;^  the  bushings  are  painted  only  part  way  across  the. batten  to  dis- 
tinguish them  from  the  cylinder  ends,  as  shown  in  fig.  825.     The  travel 


END  OF  CYLINDER      JliTRAVEL      BUSHING 


Pig.  824  and  825. — Inside  admission  piston  valve  battens.  They  are  especially  useful  to  check 
^^^.X^^ve  setting.  The  ends  of  the  cylinder  should  be  indicated  on  the  seat  battens  in 
addition  to  the  bushings. 


of  the  valve  is  ascertained  and  indicated  by  lines  which  register  as  shown 
in  the  figures;  thus  the  battens  may  be  placed  so  as  to  show  the  extreme 
positions  of  the  valve. 


450 


VALVE  SETTING 


Oues.    Of  what  particular  use  are  battens? 

Ans.  They  are  helpful  in  the  absence  of  an  indicator  to  verify 
the  setting  of  inside  admission  valves,  and  more  especially  to 
check  the  machine  work  on  the  valve  and  seat;  if  there  be  any 
errors  in  the  location  of  ports,  etc.,  they  may  be  discovered  by 
carefully  transferring  the  various  measurements  of  the  valve 
and  seat  to  battens  for  comparison. 


STEAM     P/\SSAGES 


Fig.  826. — Showing  similarity  between  the  main  valve  of  a  riding  cut  off  gear,  and  the  ordinary- 
slide  valve.  The  main  valve  is  simply  a  plain  D  valve,  having  steam  passages  S,  S'  at  its 
ends,  and  planed  on  its  back  to  form  a  seat  for  the  cut  off  valve. 

Setting  the  Riding  Cut  Off  Gear. — There  are  two  types 
of  riding  cut  off  gear  in  general  use,  the  first  having  a  movable 
(rotating)  eccentric,  and  the  second  a  fixed  eccentric,  but  having 
an  adjustable  cut  off  valve,  known  as  the  Meyer  valve.  The 
method  of  setting  the  valves  for  each  type  will  now  be  described: 


1.  The  Riding  Cut  Off,   Movable  Eccentric. 

a.  The  main  valve  is  set  in  the  same  manner  as  the  ordinary 
slide  valve. 


VALVE  SETTING 


451 


^  To  avoid  confu- 
sion, it  suffices  to 
remember  that  the 
main  valve  is  noth- 
ing more  than  an 
ordinary  D  valve 
having  steam  pass- 
ages at  its  ends,  and 
planed  on  its  back 
to  form  a  seat  for 
the  cut  off  valve. 
In  setting  the  valve, 
therefore,  the  outer 
end  walls  are  to  be 
ignored. 

The  relation  be- 
tween the  main 
valve,  and  an  or- 
dinary D  valve  is 
shown  in  fig.  826, 
the  latter  being 
illustrated  in  solid 
black  section;  the 
main  valve  has  in 
addition  to  this, 
the  portions  shown 
at  each  end  which 
contain  the  steam 
passages  S  and  S', 


b.  The  engine  is 
now  turned  in  the 
direction  in  which 
it  is  to  run,  until 
this  valve  is  in  its 
neutral   position.  * 


*NOTE.— The  reason 
for  putting  the  main  valve 
in  its  neutral  position  is 
to  facilitate  this  adjust- 
ment, as  the  necessary 
measurements  are  more 
conveniently  made  with 
respect  to  the  main  valve 
than  to  the  seat. 


452 


VALVE  SETTIN.G 


To  locate  the  neutral  position,  the  engine  is  turned  over  until  the  main 
valve  comes  in  the  extreme  positions  A  andB,  as  shown  in  fig.  827,  and  a 
reference  mark  for  each,  made  on  the  valve  stem  with  a  tram,  having  one 
end  in  a  convenient  fixed  center  P.  The  distance  A  B,  is  bisected,  giving 
the  point  M,  the  three  points  being  permanently  located  with  a  center 


EXTREME     POSITIONS    OF    CUT   OFF    VALVE 


Fig  828. — Equalizing  the  travel  of  the  riding  valve.  With  the  main  valve  in  neutral  position, 
and  cut  off  eccentric  loosened,  the  distances  E  and  F,  are  measured  for  the  two  extreme 
positions  and  the  valve  stem  adjusted  until  these  distances  become  equal. 

punch,  and  care  being  taken  that  the  points  are  in  a  straight  line  parallel 
to  the  stem. 

The  valve  is  now  placed  in  its  neutral  position,  by  turning  the  engine 
in  the  direction  of  its  rotation  until  the  point  M,  registers  with  the  end 
of  the  tram  as  shown  in  the  figure. 


c.  The  next  step  is  to  equalize  the  travel  of  the  riding  valve, 
that  is,  to  adjust  the  riding  valve  stem  or  eccentric  rod  to  the  proper 


FALVE  SETTING 


453 


length  so  that  the  valve  will  travel  an  equal  distance  each  side  of 
its  neutral  position,  j 

With  the  main  valve  in  its  neutral  position,  the  movable  eccentric  is 
loosened  on  the  shaft,  and  turned  in  the  direction  in  which  the  engine  is  to 
run  until  the  cut  off  valve  is  brought  into  its  extreme  positions  A'  and  B', 
fig.  828. 

The  distance  from  the  steam  edge  of  the  riding  valve  to  the  end  of  the 
main  valve  is  measured  for  the  two  positions.  If  the  valve  stem  be  too 
long  or  too  short  these  distances  will  be  unequal;  the  valve  stem  or  eccentric 
rod,  in  this  case,  should  be  adjusted  until  these  distances  E  and  F,  are  equal 
as  shown  in  the  figure,  f  Having  equalized  the  travel  of  the  valve,  tram 
marks  A',  B',  M',  indicating  respectively  the  extreme  and  neutral  positions, 

CUT  Orr    VALVE     CLOSING    STEAM 
P/i5SAGE    FOR       \/Z  CUT  OFF 


Fig.  829. — Riding  valve  in  cut  off  position.  To  locate  eccentric  for  any  desired  cut  off ,  turn 
engine  over  till  piston  is  at  the  desired  point  of  cut  off,  then  turn  riding  eccentric  in  the 
direction  of  motion  till  riding  valve  is  in  cut  off  position  as  shown. 

should  be  made  as  shown  in  fig.  827,  on  the  cut  off  valve  stem  with  the 
tram  center  at  P',  using  the  same  tram  as  was  used  for  the  main  valve  stem. 

d.  To  complete  the  setting,  it  remains  only  to  find  the  position 
of  the  movable  eccentric  which  will  give  the  desired  cut  off. 


tNOTE. — To  avoid  error,  it  should  be  ascertained  that  the  steam  ports  of  the  main 
valve  are  equidistant  from  the  ends;  if  not,  measurements  E  and  F,  fig.  828,  should  be  taken 
with  respect  to  the  steam  edges  of  the  cut  off  valve,  lines  being  lightly  scribed  on  the  back  of  the 
main  valve  to  indicate  the  extreme  positions. 


454 


VALVE  SETTING 


If  the  valve  gear  is  to  cut  off  at,  say  one-half  stroke,  the  engine  is  turned 
in  the  direction  in  which  it  is  to  run  to  this  point  of  the  stroke,  and  the 
movable  eccentric  turned  in  the  same  direction  until  the  cut  off  valve  has 
just  close  1  the  steam  passage  through  the  main  valve  as  shown  in  fig.  413 ; 
the  eccentric  is  now  fastened  in  position. 

e.  When  the  riding  cut  off  valve  is  operated  by  an  automatic 
governor,  as  in  many  stationary  engines,  this  last  step  is,  of  course^ 
omitted. 


THREAD^ 

\ 


I 


CUTOFF  BLOCKS 
M S 


LEFT 
HREAD 


NEGATIVE  LAP 


Fig.  830. — ^The  riding  cut  off  with  fixed  eccentric,  showing  cut  off  blocks  M,  S,  screwed  together 
when  setting  the  valves.  The  cut  off  is  latest  when  the  blocks  are  together,  dependingon 
the  negative  lap.  After  setting  the  valves,  the  blocks  should  be  fully  extended  for  earliest 
cut  off  to  see  if  there  be  any  reopening  after  cut  off  and  before  the  main  valve  has  closed. 

When  the  engine  is  provided  with  a  governor,  the  travel  of  the  cut  off 
valve  may  in  some  cases  be  more  conveniently  equalized,  by  locating  the 
center  of  the  valve  seat  with  a  line  scribed  on  the  side  or  flange  of  the 
steam  chest,  and  equalizing  the  travel  of  the  cut  off  valve  with  respect  to 
this  line  instead  of  the  main  valve.  By  this  method  it  is  not  necessary  to 
retain  the  main  valve  in  its  neutral  position  while  adjusting  the  cut  off 
valve;  hence  the  loose  eccentric  need  not  be  disconnected  from  the  governor 
in  making  this  adjustment. 


2.  The  Riding  Cut  Off:  Fixed  Eccentric. 

This  type  of  riding  cut  off  is  set  in  much  the  same  way  as 
the  preceding  form.    In  making  the  adjustments,  the  important 


VALVE  SETTlNd  455 


principle  upon  which  the  gear  is  based  should  be  understood, 
and  kept  in  mind,  viz. :  the  angular  advance  being  fixed,  the  cut 
off  is  varied  by  changing  the  lap.    The  valves  are  set  as  follows: 

a.  The  main  valve  is  set  in  the  same  manner  as  the  ordinary 
slide  valve. 

b.  To  set  the  riding  valve,  the  riding  blocks  M,  S,  are  first  screwed 
closely  together  as  shovun  in  fig.  830;  this  being  their  position  for 
latest  cut  off. 

C.  The  travel  of  the  riding  valve  is  now  equalized  by  the  method 
described  on  page  452,  and  the  riding  eccentric  located  in  the 
position  best  suited  to  the  conditions  under  which  the  engine  is 
to  be  operated. 

For  a  marine  or  reversing  engine,  the  riding  eccentric  is  set  opposite  the 
crank,  that  i^,  at  90  degrees  angular  cidvance,  since  the  motion  of  the  cut 
off  valve  is  then  correct  for  both  forward  and  reverse  motion;  in  this 
position  an  equivalent  motion  of  the  eccentric  may  be  imparted  to  the 
valve  stem  by  the  cross  head  through  a  lever,  thus  dispensing  with  the 
eccentric.  The  angular  advance  of  the  riding  eccentric  on  stationary  * 
engines  is  usually  a  little  less  than  90  degrees.  The  effect  of  reducing  the 
angular  advance  is  to  require  a  smaller  movement  for  a  given  change  of 
cutoff.  • 

The  riding  eccentric  should  be  so  located  that  it  will  give  the  most  rapid 
closure  of  the  steam  ports  for  the  cut  off  mostly  used. 

d.  The  engine  is  now  turned  over  to  see  if  there  be  any  reopening 
of  the  riding  valve  after  it  has  cut  off  and  before  the  main  valve  has 
cut  off.  Similarly  it  should  be  observed  that  there  is  no  reopening 
for  earliest  cut  off. 

e.  In  case  the  cut  off  valve  reopen  before  cut  off  of  the  main 
valve,  this  must  be  corrected  by  altering  the  position  of  the  riding 
eccentric. 

Setting  a  Link  Motion. — Adjustments  of  the  link  gear 
should  be  such  that  the  steam  distribution  will  be  favorable  to 
smooth  running  and  economy  for  the  particular  degree  of  ex- 
pansion at  which  the  engine  is  generally  run.     For  instance, 


456 


VALVE  SETTING 


engines  which  work  in  full  gear  require  a  setting  different  from 
those  which  cut  off  short ;  the  final  adjustments  therefore  should 
be  made  with  respect  to  obtaining  the  best  results  for  the  gear 
position  mostly  used.  In  general,  setting  a  link  motion  com- 
prises the  following  operations: 

1.  Equalizing  the  travel;  ' 

2.  Adjusting  the  eccentric  rods  to  uniform  length; 

3.  Finding  the  correct  positions  of  the  eccentrics; 

4.  Making  final  adjustments  for  best  steam  distribution  in  the 
gear  position  mostly  used. 


MUST     ETQUAL 


POSITION 


MID-GEAR 


Figs.  831  and  832. — Setting  the  link  motion:    1.  Equalizing  the  travel  by  adjusting  the  valve 
stem.    The  eccentrics  must  be  placed  in  extreme  position  and  link  in  mid-gear. 

Equalizing  the  Travel. — With  the  engine  on  the  dead 
center,  both  eccentrics  are  turned  on  the  shaft  to  the  extreme 
position  and  the  link  placed  in  mid-gear  as  shown  in  figs.  831 
and  832.  If  the  length  of  the  valve  stem  be  correct,  the  valve 
should  be  in  its  extreme  position,  that  is,  the  port  opening  A/ 
for  this  dead  center  should  be  the  same  as  port  opening  B,  for 
the  opposite  center. 

In  case  the  port  openings  be  unequal,  the  travel  of  the  valve  must  be 
equalized  by  adjusting  the  length  of  the  valve  stem,  or  the  eccentric  rods, 
whichever  be  the  more  convenient. 


Adjusting  the  Eccentric  Rods  to   Uniform  Length. — 

Both  eccentric  rods  should  be  of  the  same  length,  and  probably 


VALVE  SETTING  457 


will  be  when  not  made  adjustable.  If  both  rods  be  of  the  same 
length,  the  position  of  the  valve  is  unchanged  for  either  full 
gear  position  when  the  engine  is  on  the  dead  center  and  the  ec- 
centrics are  in  the  extreme  position. 

To  adjust  the  eccentric  rods  to  uniform  length,  the  engine  is  placed  on 
the  dead  center,  with  the  link  in  full  gear  and  the  eccentrics  in  the  extreme 
position  as  shown  in  fig.  833. 

The  position  of  the  valve  or  stem  is  marked  in  such  a  way  that  any 
movement  in  either  direction  can  be  measured.  If  both  rods  be  of  the  same 
length,  the  mark  on  the  valve  stem  will  return  to  its  original  position  when 


FORWARD     FULL    GEAR 

Fig.  833. — .Setting  the  link  motion:  2.  Adjusting  the  eccentric  rods  to  uniform  length.  The  link 
is  placed  in  forvyard  full  gear  position.  If  rods  be  equal  position  of  valve  should  be  the  same 
when  link  is  shifted  to  reverse  full  gear. 

the  link  is  shifted  to  its  opposite  or  reverse  full  gear  position ;  if  the  mark 
be  displaced  in  either  direction  the  reverse  rod  should  be  adjusted  until 
the  line  returns  to  its  original  position.  It  is  rarely  necessary  to  make 
this  adjustment,  except  when  a  gear  has  been  completely  dismantled. 

Finding   the   Correct   Positions   for   the   Eccentrics. — 

With  the  engine  on  either  center,  the  link  is  placed  in  the  for- 
ward full  gear  position,  and  the  eccentrics  turned  from  the 
extreme  position  until  they  are  at  right  angles  with  the  crank, 
that  is,  where  the  angular  advance  equals  zero  as  shown  in 
fig.  834.  The  forward  eccentric  is  now  turned,  in  the  direction 
of  forward  rotation,  until  the  valve  shows  the  desired  lead  as 
in  fig.  835. 

Similarly,  the  link  is  shifted  to  the  reverse  full  gear  position,  fig.  836, 
and  the  reverse  eccentric  turned,  in  the  direction  of  reverse  rotation,  until 


458 


VALVE  SETTING 


the  proper  lead  is  obtained  as  shown  in  fig.  837.  Each  eccentric  is  fastened 
after  locating  its  position,  and  the  results  tested  by  trying  the  leads  for  the 
opposite  centers,  which  completes  the  setting  for  engines  operating  in  full 
gear. 


7ER0    /ANGULAR   ADVANCE 


NEUTRAL    POSITION 


FORWAf=^D    FULL    GEAR 

Fig.  835. — Setting  the  link  motion:  3.  Locating  the  eccentrics — first  step:  Both  eccentrics  are 
placed  at  zero  angular  advance,  that  is  at  right  angles  to  the  crank,  bringing  valve  into 
neutral  position. 

Final  Adjustments. — For  engines  which  use  the  link  motion 
as  a  variable  expansion  gear,  the  best  results  are  obtained 
when  the  valve  is  set  to  give  the  proper  lead  for  the  ''running 
cut  off." 


LEAD    POSITION 


FORWARD    EOC.  ADVANCED 


FORWARD    FULL    GEAR 

Fig.  834. — Setting  the  link  motion:  3.  Locating  the  eccentrics — second  step:  With  link  in 
forward  full  gear,  the  forward  eccentric  is  advanced  until  valve  shows  proper  lead,  bringing 
valve  into  its  forward  linear  advance  position. 

This  applies  especially  to  locomotives  and  engines  which  usually  run 
with  a  considerable  degree  of  expansion.  Since  the  lead  increases  from 
full  to  mid-gear,  it  is  obvious  that  if  it  be  correct  in  full  gear,  it  will  be  too 
great  when  hooked  up  for  short  cut  off  working. 


The  lead  may  be  corrected  for  the  running  cut  off,  by  placing 
the  link  in  the  running  position,  and  setting  back  the  forward 


VALVE  SETTING 


459 


or  reverse  eccentric,  or  both,  in  equal  or  unequal  amounts  until 
the  desired  lead  is  obtained. 

The  particular  method  of  correcting  the  lead  depends  on  the  conditions 
of  service.  For  engines  which  run  mostly  in  forward  gear,  as  express 
passenger  engines,  it  is  of  little  importance  if  both  eccentrics  have  the  same 


NEUTRAL 
POSITION 


REVERSE    FULL    GZ^^ 


Fig.  836. — Setting  the  link  motion:   4.  Locating  the  eccentrics — third  step: 
to  reverse  full  gear  position,  bringing  valve  back  to  its  neutral  position. 


The  link  is  shifted 


angular  advance,  however,  for  suburban  tank  locomotives,  or  those  running 
considerable  distances  in  each  gear  both  eccentrics  should  have  the  same 
angular  advance. 


LEAO   POSITtON 


REVERSE    ECC-   ADVANCED 

Fig.  837.7— Setting  the  link  motion:  4.  Locating  the  eccentrics — fourth  step:  The  reverse 
eccentric  is  advanced  until  the  valve  shows  the  proper  lead;  this  moves  the  valve  to  its 
reverse  linear  advance  position  which  completes  the  setting  except  when  final  adjustments 
are  made  to  adopt  the  link  motion  to  special  running  conditions. 

The  following  table  shows  the  practice  of  several  railroads 
with  respect  to  the  lead. 


NOTE. — When  the  link  block  is  at  one  end  of  the  slot,  the  valve  partakes  of  the  motion 
of  the  eccentric  attached  to  that  end  of  the  link.  When  the  block  is  not  at  the  end  of  the  slot, 
the  valve  partakes  of  the  combined  motion  of  the  two  eccentrics,  being  the  equivalent  of  a 
virtual  eccentric  of  decreased  throw  and  increased  angular  advance. 

NOTE. — The  object  in  curving  a  link  block  is  to  equalize  the  lead  for  all  travels  of  the 
valve.  To  accomplish  this  it  is  necessary  to  have  the  radius  of  curvature  of  the  slot  such  as 
will  make  the  increase  or  decrease  of  the  lead  the  same  for  both  strokes  of  the  piston. 


460 


VALVE  SETTING 


Table  of  Leads  for  Locomotives 

Forward 
full  gear 

Reverse 
full  gear 

Lead  for 
running 
cut  off 

Illinois  Central      

+  H2 

+Hi 

Chicago  &  Northwestern  (Allen  Valves) .  . 

-Vm 

+  H 

New  York,  Hew  Haven  &  Hartford.  . .  . 

■       +^^6 

-M 

+M 

Lake  Shore  &  Michigan  Southern 

-Vi^ 

-% 

+^/l6 

Chicago  Great  Western { 

zero 

zero 

8/i6tO% 

*For  Mogul  freight  engines;   with  this  exception  the  data  in  the  table  relates  to  passenger 

nnfivpf;. 


locomotives. 


The  diverse  settings  given  in  the  table  are  due  chiefly  to  the  peculiarities 
of  the  several  designs;  the  length  of  the  eccentric  rods  has  a  marked 
influence  on  the  methods  followed  in  the  different  cases.  It  should  be 
noted  that  the  several  railroads  substantially  agree  on  the  amount  of  lead 
for  the  running  cut  off. 


Valve  Setting  with  the  Indicator. — ^An  important  use  of 
the  indicator  is  to  check  the  valve  setting,  for  if  the  adjustments 
be  not  correct,  the  errors  can  be  plainly  located  by  taking  cards. 
The  accompanying  cards  show  the  distortions  produced  by 
various  adjustments. 


In  setting  a  valve,  changes  in  the  steam  distribution  can  be  effected, 
either  by  shifting  the  position  of  the  eccentric  upon  its  shaft  or  by  length- 
ening or  shortening  one  or  more  of  the  rods  connecting  the  eccentric  with 
the  valves.  The  result  attained  in  either  case  should  be  clearly  under- 
stood, since  if  it  be  attempted  to  make  the  needed  adjustments  in  the 
wrong  place,  the  engine  may  be  put  in  worse  condition  than  it  was  originally. 

Changing  the  regular  position  of  the  eccentric  either  hastens  or  retards 
the  action  of  the  valves.  Moving  the  eccentric  ahead  makes  all  the  events 
of  the  stroke  which  are  dependent  upon  the  eccentric  come  earlier  in  the 
stroke,  while  moving  back  the  eccentric  causes  all  the  events  to  occur 
later  in  the  stroke. 


VALVE  SETTING 


461 


Figs.  838  to  848. — Effects  of  valve  adjustments  as  recorded  by  indicator  diagrams.  Card 
No.  1  was  taken  when  the  eccentric  had  the  proper  angular  advance  of  a  little  more  than 
90  degrees  (in  the  case  of  a  single  eccentric  Corliss  engine)  and  cut  off  and  compression  were 
made  as  nearly  equal  as  possible.  In  card  No.  2  the  angular  advance  was  increased.  In 
card  No.  3  the  angular  advance  was  made  still  greater.  In  card  No.  4  the  eccentric  was 
shifted  back  so  that  there  was  no  angular  advance.  Card  No.  5  is  a  crank  end  card  and 
was  taken  when  the  eccentric  was  moved  way  back  and  gave  a  negative  angular  advance. 
The  diagram  was  traced  in  the  direction  indicated  by  the  numbers.  Admission  occurs  at 
1,  cut  off  at  2,  release  at  3.  Card  No.  6  is  a  similar  diagram  from  the  head  end.  In  card 
No.  7  the  eccentric  is  moved  back  and  the  rods  adjusted  to  give  correct  steam  distribution  and 
then  under  these  conditions  the  eccentric  card.  No.  8,  was  taken.  In  this  case  the  indicator 
derived  its  motion  from  the  eccentric  rod  instead  of  from  the  cross  head  and  the  diagram 
shows  the  working  of  the  valves  of  the  engine,  when  the  indicator  drum  is  moving  at  its 
greatest  speed;  and  thus  any  peculiarities  m  the  action  of  the  valve  are  magnified.  Com- 
pression and  release  come  near  the  middle  of  the  card  and  are  spread  over  a  considerable 
length.  In  card  No.  9  the  head  end  exhaust  rod  was  lengthened  and  there  is  too  much 
compression  at  a.  In  No.  10  the  rod  is  made  still  longer.  In  card  No.  11  the  head  end 
exhaust  rod  is  made  too  short  and  there  is  too  little  compression  at  b. 


NOTE. —  When  setting  an  eccentric,  a  rule  that  can  be  easily  remembered  is:  Set  the 
eccentric  far  enough  ahead  of  a  right  angle  to  the  crank  to  allow  for  the  lap  and  lead  of  the  valve. 
The  mistake  of  turning  the  eccentric  "just  half  way  around"  to  reverse  the  engine  should  not 
be  made. 

NOTE. — An  engine  properly  built,  and  not  run  at  too  high  a  rotative  speed,  will  run 
smoothly  with  a  moderate  amount  of  compression.  To  attempt  to  get  smooth  running  with 
an  extra  amount  of  compression  or  lead  means  more  oil,  more  coal,  and  more  repairs. 


462  VALVE  SETTING 


In  the  Corliss  engine  the  point  of  cut  off  is  determined  by  the  governor 
instead  of  by  the  eccentric,  and  so  only  the  points  of  admission,  release 
and  compression  are  affected  by  shifting  the  eccentric.  In  the  case  of  a 
slide  valve  engine  it  affects  all  the  events. 

In  a  slide  valve  engine  an  adjustment  of  the  length  of  the  eccentric  or 
valve  rod  simply  changes  the  position  of  the  valve  so  that  it  will  have  more 
lap  or  lead  at  one  end  than  before,  and  less  lap  or  lead,  as  the  case  may  be, 
at  the  other  end. 

In  the  Corliss  engine  an  adjustment  of  the  eccentric  rod  produces  the 
same  result,  increasing  or  decreasing  the  lap  or  lead,  as  the  case  may  be, 
at  one  end  of  the  stroke,  while  it  has  the  opposite  effect  at  the  other  end. 

The  lengths  of  the  eccentric  rod  or  gab  rod  on  a  Corliss  engine,  however, 
should  never  be  changed,  unless  it  is  found  that  the  intermediate  rocker 
and  wrist  plate  do  not  travel  equally  on  each  side  of  a  vertical  center  line. 

All  the  rod  adjustment  should  be  made  in  the  radial  rods  extending  from 
the  wrist  plate  to  the  four  valves.  Adjusting  any  of  these  rods,  of  course, 
affects  only  the  valve  to  which  each  rod  is  connected  and  will  give  greater 
or  less  lap  to  that  valve,  according  as  it  is  lengthened  or  shortened. 

If  more  lap  were  given  to  an  exhaust  valve  in  this  way,  for  example, 
the  valve  would  open  later  and  compression  would  occur  earlier,  since  the 
valve  would  close  earlier.  The  port  opening  would  also  be  less.  If  less 
lap  were  given  to  the  valve  the  reverse  of  these  conditions  would  be  true. 


INDEX  OF  GUIDE  No.  1 


READY  REFERENCE 

INDEX 


Absissoe,  def.,  58,  59. 
Absolute,  pressure,  17. 

steam  engine,  61. 

temperature,  def.,  21. 

zero,  21,  35. 
Actual  cut  off,  def.,  197. 

mean  effective  pressure,  73. 
Absorption  dynamometer,  93. 
Adiabatic  expansion,  54. 
Admission,  area,  formula,  70. 

double,  ills.,  294. 

inside,  ills.,  292. 

outside,  ills.,  292. 

pistcm  valve,  ills.,  292,  299. 

inside,  setting,  ills.,  444-446. 

quadruple,  305. 

slide  valve,  def.,  19G. 
modified,  ills.,  292. 
open,  ills.,  195. 
position,  ills.,  197. 
Advance,  angular,  238,  245,  441-445. 

linear,  eccentric,  ills.,  238. 
Allen,  link,  ills.,  334,  335. 

valve,  ills.,  208,  209. 
principles,  294. 
American  Ball,  cut  off,  ills.,  253. 

rock  shaft,  ills.,  231. 

variable  speed  mechanism,  ills.,  399. 
American  pump  valve  gear,  ills.,  430. 
Ames,  connecting  rod,  ills.,  149. 

cross  head,  ills.,  139. 
Angular  advance,  eccentric,  237,  238. 

method  of,  finding,  des.,  ills.,  441-445. 

variable  cut  off,  245. 
Angularity,   of  connecting  rod,  effect,  des., 

ills.,  154. 
Apparent  cut  off,  ills.,  196,  197. 
Area,  admission,  formula,  70. 

circle,  formula,  80. 
Armington  and  Sims  valve,  295. 
Asymptotes,  ills.,  60. 
Atlas  steam  engine,  ills.,  54. 
Atomic  weight,  1.  ^ 

Atmospheric,  engine,  Ncwcomen's,  ills.,  36. 

pressure,  def.,  2,  13,  14. 

barometer  readings,  18-20. 
variability,  15. 


Automatic,  cut  off,  engine,  def.,  243. 

governor,  Nordberg,  ills.,  390. 
throttle  valve,  def.,  383. 
Auxiliary,  governor  devices,  397. 
piston  pump,  ills.,  413. 
valve  pump,  ills.,  413. 
Axes,      rectangular,      equilateral     parabola, 
ills.,  60. 


B 


Back  pressure,  ills.,  68,  def.,  69. 
Balanced  slide  valve,  187,  291. 

Richardson,  ills.,  291. 
Balancing  cylinder,  steam  engine,  ills.,  300. 
Ball  and  Wood  connecting  rod,  ills.,  142. 
Ball,  governor,  ills.,  389. 

speed  ranger,  ills.,  382. 

valve,  ills.,  307. 
Band  fly  wheel,  176. 
Barometer,  ills.,  13,  15,  18,  19. 
Battens,  valve,  ills.,  426,  449,  450. 
Bearings,  165-17i. 

brasses,  142-144,  146,  230. 

liner  adjustment,  main,  ills.,  166. 

locomotive,  ills.,  169. 

main,  99. 

marine,  ills.,  171. 

outboard,  pillow  block,  ills.,  170. 

requirements,  165. 

self  oiling,  ills.,  170. 

simple,  165. 

two  piece,  167. 
Bilgram  diagram,  211,  213. 

application,  276. 

main  valve,  264,  268,  279. 

mid-admission,   289. 

riding  cut  off,  288.  ^ 
Blake  pump,  valve  gear,  ills.,  411. 
Boiler,  elementary,  ills.,  17. 

pressure,  65. 
Boiling  point,  ills.,  2,  3,  13,  28,  34. 
Bolt,  crank  shaft,  taper  flange,  ills.,  164. 
Bonnet,  valve,  ills.,  99. 
Box,  journal,  locomotive,  ills.,   169. 

link,  ills.,  329. 

piston,  ills.,   117,   119. 


II 


INDEX  OF  GUIDE  No.  1 


Boyle's  law,  ills.,  54,  55. 
Brake,  horse  powers  93,  94. 

prony,  ills.,  93. 

rope,  ills.,  95. 
Brasses,  142,  143,  230. 
Bremme  gear,  des.,  ills.,  352-355. 
British  thermal  unit,  def.,  8. 
Brown  engine,  cross  head,  ills.,  234. 
Brownell  steam  engine,  121,  184,  185,  231. 
Buckeye,  governor,  ills.,  396. 
Buffalo,  pump,  valve  gear,  ills.,  405. 

steam  engine,  ills.,  83. 

governor,  ills.,  249. 
Bull  ring,  ills.,  116. 
Burnham  pump,  valve  gear,  ills.,  424. 


Calipers,  use  of,  ills.,  441. 
Cameron  pump,  valve  gear,  ills.,  408. 
Card,  indicator,  see  Indicator  diagram. 
Center,  crank  shaft,  des.,  160. 

dead,  steam  engine,  151,  435. 
Centigrade  scale,  ills.,  120. 
Centrifugal,   control,  shaft    governors,    ills., 
364,  376,  378,  392-397. 

force,  des.,  174. 
Chandler  &  Taylor,  engine,  121,  206,  404. 
Circle,  area,  formula,  80. 
Clark  governor,  ills.,  397. 
Clearance,  58,  59,  75,  106. 
Clyde  cross  head,  ills.,  39. 
Compound  engine.  Reeves,  section,  ills.,  299. 
Compression,  201. 

curve,  ills.,  56. 
Cone,  governor.  Ball  engine,  ills.,  398. 

piston,  ills.,  119,  120. 
Condensation  of  steam,  33,  34,  37,  196. 
Condenser,  elementary,  parts,  38. 
Condensing  steam  engine,  def.,  47. 
Conduction,  heat,  ills.,  6. 
Connecting  rod,  ills.,  141-156. 

action  on  crank  pin,  152. 

Ames,  ills.,  149. 

angularity,  ills.,  154,  190. 

Ball  and  Wood,  ills.,  142. 

built  up,  ills.,  146,  147. 

composition,  142. 

Eclipse  Corliss,  ills.,  141. 

hatchet  end  type,  des.,  ills.,  149. 

length,  142. 

marine,  ills.,  144,  145. 

Phoenix,  ills.,  144. 

Sturtevant,  ills.,  150. 

Westinghouse,  ills.,  150. 
Conservation  of  energy,  laws,  12* 
Constant,  expansion,  diag.,  66. 

horse  power,^  87-89. 
Constant  lead,  slide  valve,  193. 
Co-ordinates,  def.,  59. 
Convection,  heat,  ills.,  6. 
Corliss  engine,  connecting  rod,  ills.,  143. 

fly  wheel,  ills.,  174,  175. 

gibs,  ills.,  132. 


Corliss  engine, — Continued 
indicator  card,  76. 
Murray,  parts,  ills.,  99,  170. 
Cotters,  connecting  rod,  ills.,  146,  147. 
Counter-weight,  steam  engine,  use,  160. 
Crank(s),  angular  position,  ills.,  263. 
arm,  dimension,  158,  160. 
compared  with  eccentric,  ills.,  237. 
end,  steam  engine,  def.,  90. 
key,  ills.,  158. 

pin,  action  on,  ills.,  151-154,  158,  159. 
position,  during  one  stroke,  ills.,  52. 
to  obtain,  diag.,  267. 
transferring,  264. 
sequence  of,  des.,  164. 
shaft,  156-164. 
Cross  head,  pump,  418,  419. 
steam  engine,  49,  127. 
Amesy  139. 

attachment  methods,  141. 
Brown  engine,  ills.,  134. 
Corliss,  Fishkill,  ills.,  137. 
Fulton,  ills.,  138. 
Harris,  ills.,  140. 
Murray,  ills.,  135. 
hoisting  engine,  Clyde,  ills.,  139. 
locomotive,  des.,  ills.,  136. 
marine,  ills.,  134. 
Porter- Allen,  ills.,  135. 
Reeves,  ills.,  132. 
split  type,  ills.,  140. 
,  stationary  engine,  135. 

Crossed  rods,  link  motion,  ills.,  322,  325. 
Cut  off,  63. 

actual,  197. 

affected  by  angularity  of  rod,  155. 

apparent,  63,  98,  196. 

crank,  212,  270; 

early,  ills.,  244. 

defects,  ills.,  254,  256. 
varied,  207. 
gear,  259,  279,  282. 
Rider,  ills.,  259. 
riding,  ills.,  450-454. 
Gonzenbach,  258. 
governors,  388. 

automatic,  Nordberg,  ills.,  390. 
independent,  253. 

link  motion,  ills.,  328,  329. 
parts,  256. 
late,  ills.,  244. 
marine  engine,  328. 
real,  63,  98,  196,  197. 
riding,  257,  262,  278. 

angular  advance,  263. 

fixed  eccentric,  ills.,  453,  454. 

inside  and  outside  edges,  ills.,  262, 

movable  eccentric,  450. 

neutral  position,  ills.,  451. 

setting,  ills.,  450-454. 

sluggish,  271. 

travel,  equalizing,  ills.,  452. 

variable,  262. 

angular  advance,  275. 
lap,  287. 
Stephenson  link,  326. 


INDEX  OF  GUIDE  No.  1 


III 


Cut  off,  variable, — Continued 
travel,  290. 
variable,  243-290. 
early,  254-256. 
gear.  Rider,  ills.,  259. 
principles,  245. 
riding,  262, 
shifting,  eccentric,  ills.,   246,  247, 

251,  252. 
swinging  eccentric,  ills.,  248-252. 
offset,  251. 
various,  ills.,  63. 
Cylinder,  steam  engine,  103-109. 
balancing,  ills.,  300. 
calculations,  97. 
dimensions,  94,  99,  102. 
high  speed  engine,  ills.,  184. 
insulation,  106. 
jacketted,  ills.,  107-109. 
operation,  106. 
parts,  ills.,  104,  105. 
pressure  springs,  ills.,  117,  119. 
size,  94,  99,  102. 


D  valve,  ills.,  179,  188. 

Davidson  pump,  valve  gear,  ills.,  410,  413. 

Dead  center,  steam  engine,  151. 

locating,  ills.,  434,  435. 
Deane  pump,  valve  gear,  ills.,  406,  ills.,  422. 
Diagram  factor,  ills.,  74-77. 
Diameter  cylinder,  99. 

fly  wheel,  173. 
Double,  admission  piston  valve,  294,  295. 
ported  valve,  ills.,  295,  299,  300-302. 
Dry  steam,  def.,  24. 
Duplex,  metallic  packing,  ills.,  110. 

pump,  cross  head  centers,  418,  419. 
rocker  arm,  ills.,  428. 
valve  gear,  ills.,  415-417. 

setting,  425-432. 
Worthington,  small,  ills.,  418. 
Dynamometer,  absorption,  93. 


Early  cut  off,  207. 
Eccentric,  243,  246,  248,  251. 

angular  advance,  237. 

Heilman  gear,  ills.,  247. 

key,  ills.,  137,  141. 

large,  ills.,  240. 

linear  advance,  ills.,  238. 

loose,  ills.,  309-316. 

marine,  loose,  ills.,  312,  313. 

objections,  238. 

offset,  swinging,  251. 

valve  gear,  ills.,  229. 

position,  during  one  stroke,  ills.,  52. 
finding,  437,  438. 

reversing,  ills.,  309-316. 


Eccentric, — Continued 
riding,  279. 
rod(s),  226,  233-242. 

connections,  ills.,  234. 
double  reach,  ills.,  319. 
Erieco,  des.,  ills.,  242. 
formula,  242. 

high  speed  engine,  ills.,  235. 
marine,  235,  241. 
open  and  crossed,  322-325. 
outside,  ills.,  235. 
rectangular,  ills.,  234. 
shifting,  ills.,  246-248. 
strap,  ills.,  226,  229,  234,  235,  236,  239, 

241    242. 
swinging,  248-252. 
throw,  236. 
various,  241. 
virtual,  277. 
Eccentricity,  slide  valve,  ills.,  203. 
Eclipse  Corliss  connecting  rod,  ills.,  141. 
Effective  pressure,  73. 
Energy,  conservation  of,  9,  11,  12. 
Engine,  see  Steam  engine. 
Equal  lead,  slide  valve,  194. 
Erieco  engine,  crank  shaft,  ills.,  162. 
Exhaust,  arch,  ills.,  186. 

cavity,  ills.,  104,  217,  280,  291. 
edge,  ills.,  181,  182,  186,  280,  446. 
lap,  ills.,  180,  188,  301. 
lead,  193. 

lines,  long,  pipe  for,  217. 
opening,  ills.,  199,  204,  215,  306. 
passage,  ills.,  104,  181,  182,  294,  295. 
port,  ills.,  104,  105,  180,  181,  182,  184, 
214,  215. 
Expansion  of  steam,  53. 
adiabatic,  54. 
constant,  66-67. 
curve,  57,  62. 

hyperbolic,  58,  59.  • 
theoretical,  61,  62. 
gain,  steam  engine,  62. 
isothermal,  54. 
number,  64- 
rules,  64. 
Expansion,  valve  gears,  243. 

of  water,  27. 
Expected,  and  theo.  card,  Corliss  engine,  76. 

mean  effective  pressure,  76. 
External  latent  heat,  steam,  ills.,  30,  31. 


Factor  diagram,  74-77. 

Fahrenheit  scale,  def.,  ills.,  20. 

Fink  link,  des.,  ills.,  336,  337,  338. 

Fishkill- Corliss  engine,  cross  head,  ills.,  137. 

Pitchburg  governor,  ills.,  393. 

Fly  wheel,  steam  engine,  48-50,  171-178. 

Buft'alo,  249. 
Follower  ring,  ills.,  116. 
Foot-poimd,  def.,  9. 


IV 


INDEX  OF  GUIDE  No.  1 


Force,  centrifugal,  174,  376. 
formula,  368. 

freezing,  water,  ills.,  28. 

parallelogram,  component,  151,  153. 

resultant,  ills.,  151. 
Forged  center  crank  shaft,  ills.,  161. 
Formula (ae),  centrifugal  force,  368. 

circle,  area,  80. 

cylinder  dimensions,  97,  99,  102. 

fly  wheel  speed,  178.  c 

governor,  369,  370,  371. 

horse  power,  78,  81-85,  92,  94,  95. 

pressure,  mean  effective,  102. 

steam,  expansion,  54,  62. 
port  area,  183. 
volume  of  superheated,  46. 

thrust,  piston,  152. 

valve  stem,  Seaton's,  226. 
Forward  pressure,  ills.,  68. 
Freezing  point,  water,  ills.,  2,  28. 
Fulton- Corliss  cross  head,  ills.,  138. 
Fusion,  ills.,  27,  28. 


Gallon,  water,  U.  S.,  weight,  4. 

Gardner  governor,  ills.,  384,  385,  387. 

Gaseous  matter,  ills.,  24. 

Gauge,  steam,  ills.,  16-18. 

Gear,  see  Valve  gear. 

Gib,  steam  engine,  127,  131,  132,  137,  148. 

Giddings  valve,  ills.,  301. 

Gonzenbach  cut  off  valve,  ills.,  257-261. 

Gooch  link,  des.,  318. 

Governor (s),  steam  engine,  363-402. 

auxiliary  devices,  397. 

centrifugal,  364,  376,  378,  396,  397. 

classes  of,  363. 

close  regulation,  391. 

cone,  ills.,  398. 

cut  off,  388,  390. 

hunting,  374. 

inertia,  375,  diag.,  376. 

isochronous,  374. 

loaded,  369-371. 

parabolic,  373,  374. 

pendulum,  365,  374. 

regulation,  379,  390. 

Riblet,  ills.,  378. 

Rites,  ills.,  392. 

Russell,  ills.,  397. 

sensitiveness,  371. 

shaft,  392-397. 

speed  control,  401. 

spring,  377,  381. 

ball,  Hartwell,  ills.,  389. 

stability,  372-375. 

swinging  eccentric,  249. 

throttling,  ills.,  380-387. 

troubles,  402. 

variable  speed,  398. 
Gudgeon,  def.,  150. 
Guide,  steam  engine,  ills.,  134-136. 

valve  stem,  ills.,  230,  231. 


H 


Hackworth  gear,  des.,  ills.,  340-348. 
Harris- Corliss,  engine  parts,  107,  174,  175. 
Harrisburg  governor,  ills.,  393. 
Hartwell  governor,  ills.,  389. 
Head  end,  steam  engine,  def.,  90. 
Heat,  d^.,  5. 

conduction,  ills.,  6. 

convection,  ills.,  6. 

latent,  def.,  5.  _ 

mechanical  equivalent,  ills.,  10. 

specific,  def.,  6. 

measurement,  8. 

radiation,  ills.,  6. 

sensible,  def.,  5. 

steam,  30,  31. 

transfer  of ,  6. 

unit,  8,  10. 
Heilman  gear,  ills.,  247. 
High  speed  engine,  96. 

parts,  119,  184,  235. 

Erie  City,  ills.,  232. 
Hollow  piston,  Murray-Corliss,  ills.,  118. 
Hoosier  throttling  governor,  ills.,  382. 
Horizontal  engine,  automatic  cut    off,  233. 

parts,  ills.,  48. 
Horse  power,  belt,  176. 

brake,  79,  93. 

calculations,  80,  81 

constant,  87-89. 

def.,  12,  78. 

electrical,  def.,  79. 

formulae,  78,  81-85,  92,  94,  95. 

indicated,  def.,  79. 

nominal,  def.,  78. 

piston  rod,  effect,  90. 

S.  A,  E.,  def.,  79. 

table,  90. 
Hot  wire  instrument,  Whitney,  ills.,  7. 
Houston  Stanwood  &  Gamble  steam  engine, 

ills.,  57,  126,  187,  188. 
Hydraulics,  principles,  3,  4. 
Hydrostatic  paradox,  ills.,  4. 
Hyperbola,  def.,  58. 
Hyperbolic,  curve,  58-60. 

logarithms,  70,  71. 


I 


Ice,  fusion,  heat  energy,  27,  28. 

specific  gravity,  volume  and  weight,  1. 

to  steam,  ills.,  24-32. 
Ide  double  port  valve,  ills.,  295. 
Ideal  engine,  eccentric  strap,  des.,  240. 
Independent  cut  off  valve  gear,  260. 
Inertia,  control,  ills.,  394,  395. 

def.,  172,375. 

governor,  ills.,  375,  376. 
Indicated  horse  power,  79. 
Indicator,  steam  engine,  ills.,  85,  91,  92. 

valve  setting  with,  460-462. 


INDEX  OF  GUIDE  No,  1 


Indicator  diagram,  back  pressure,  68. 

compression,  56. 

construction,  55,  56,  58,  59,  66,  85,  87. 

Coliss  engine,   76. 

cut  off,  various,  63. 

diagram  factor,  75. 

expansion,  58,  59,  61,  66. 

expected  card,  101. 

hyperbolic  logarithm,  70. 

initial,  pressure,  64. 

mean  J  effective  pressure,  69,  70,  87. 
forward  pressure,  68. 

steam  expansion,  advantage,  61,  62. 

summation  of  ordinates,  87. 

terminal  pressure,  65,  67. 

throttling  governor  action,  386. 

valve  adjustments,  461. 

various  losses,  74. 
Indirect,  rocker,  Erie  City  engine,  ills.,  232. 

valve  gear,  233. 
Initial,  condensation,  def.,  196. 

pressure,  steam  engine,  diag.,  64,  65. 
Inside,  admission,  ills.,  292. 

valve  setting,  des.,  ills.,  444-446. 

cut  off  edges  of  valve,  ills.,  262. 

lap,  ills.,  189,  198,  200. 

lead,  193. 
Internal  latent  heat,  des.,  ills.,  30,  31. 
Isochronous,  governor,  374. 
Isothermal  expansion,  54. 


J 


Jacketed  cylinders,  steam  engine,  107,  108. 

Joule's  equivalent,  10. 

Journal  box,  locomotive,  ills.,  169. 

Joy  valve  gear,  ills.,  355-359. 

Judson  throttling  governor,  parts,  ills.,  380. 

Junk  packing,  ills.,  114. 


K 


Key,  crank,  proportions,  158. 

cross  head,  141. 

piston  rod,  123. 
Key  way,  shaft,  ills.,  157. 
Kinetic  energy,  ills.,  11,  12. 
Knowles  pump,  valve  gear,  ills.,  409. 


Laidlaw-Dunn-Gordon  pump,  valve  gear,  420. 
Lap,  exhaust,  ills.,  180,  188. 

formulae,  212. 

inside,  ills.,  188,  189,  198,  200. 

latest  cut  off,  281. 

Marshall  gear,  ills.,  350. 

negative,  189,  190,  210,  262,  275,  282. 

outside,  ills.,  188. 

positive,  ills.,  189,  190. 

variable,  278. 


Latent  heat,  5,  27,  29. 
Lead,  191,  192. 

equal,  194. 

equalizing,  ills.,  437,  438. 

Hackworth  gear,  ills.,  342,  343,  344,  346. 

inside,  200. 

link  motion,  effect  on,  323-325,  335. 

Marshall  gear,  348. 

measurement,  436. 

negative,  192,  193,  436. 

positive,  ills.,  436. 

variable,  194. 
Leffel  engine,  valve  and  valve  gear,  252,  302. 
Lentz  poppet  valve  engine,  valve  gear,  251. 
Lidgerwood  hoisting  engine,  link  motion,  323. 
"Line  and  line"  position,  ills.,  190. 
Linear  advance,  ills.,  206,  212,  238. 
Link  motion,  317-338. 

Allen,  ills.,  334,  335. 

Fink,  ills.,  336,  337,  338. 

Gooch,  des.,  318. 

independent  cut  off,  ills.,  328,  329. 

length,  332. 

marine  engine,  ills.,  319,  320. 

Reeves,  ills.,  326. 

rods  open  and  crossed,  ills.,  322-325. 

setting,  ills.,  455,  460. 

Stephenson  (so  called),  317,  318,  326. 

shifting,  318,  319,  327. 

slip,  def.,  331. 

stationary,  332-334. 

suspension,  ills.,  330,  331. 

Williams,  des.,  ills.,  317. 
Loaded  governor,  construction,  371. 
Locomotive,  cross  head,  des.,  ills.,  136. 

driving  journal  box,  ills.,  169. 

valve,  setting,  460. 
gear,  360. 

link,  ills.,  321,  330. 
Walschaerts,  360. 
Logarithms,  hyperbolic,  70,  71. 
Loose  eccentric  reversing  gear,  ills.,  309-315. 
Lost  motion,  pump,  valve  gear,  429. 


McEwen  engine  governor,  ills.,  391. 
McGowan  pump,  valve  gear,  ills.,  431. 
Mcintosh  &  Seymour  governor,  ills.,  396. 
Main  bearings,  165-171. 
Marine  engine,  bearing,  171. 

connecting  rod,  ills.,  144,  145. 

crank  shaft,  des.,  164. 

cross  head,  ills.,  132. 

eccentric  rod,  235. 

piston,  ills.,  119. 
rod,  ills.,  124. 

triple  expansion,  Raabe,  ills.,  316. 

valve  gear,  link,  319,  320,  327,  328. 

reversing,  loose  eccentric,  312,  313. 
Marshall  gear,  ills.,  348-352. 
Mean,  effective  pressure,  68. 

expected  pressure,  76. 
Metallic  packmg,  ills.,  110. 


VIII 


INDEX  OF  GUIDE  No.  1 


Steam  engine, — Continued 
Atlas,  ills.,  54.^ 

atmospheric,  Newcomen's,  ills.,  36. 
automatic,  187,  243. 
back  pressure,  ills.,  68,  def.,  69. 
"balancing  cylinder,  ills.,  300. 
basic  principles,  l-;-46. 
bearings,  see  Bearings, 
belt,  power  transmitted,  rule  176. 
brakeis) ,  horse  power,  formula,  94. 

ills.,  99,  142,  143,  230. 
Bremme  gear,  forward  motion,  353. 
Buffalo,  ills.,  83. 
chest,  ills.,  181. 
calculations,  98,  99,  100,  101. 
classes,  47. 

compound.  Reeves,  ills.,  299. 
compression,  ills.,  200,  202. 
condensation,  initial,  196. 
condensing,  47. 
connecting  rody  ills.,  141-156. 

angularity,  154,  190. 
Corliss,  connecting  rod,  ills.,  141. 

fly  wheel,  ills.,  174,  175. 

gibs,  ills.,  132. 

indicator  card,  76. 

Murray,  outboard  bearing,  170. 

parts  of,  ills.,  99. 
counter- weight,  160. 
crank,  see  Crank, 
cross  head,  see  Cross  head, 
cut  off,  see  Cut  off. 
cylinder,  see  Cylinder, 
dead  center,  151,  434,  435. 
diagram,  see  Indicator  diagram. 

factor,  ills.,  74-77. 
eccentric,  see  Eccentric, 
efficiency  calculations,  55-102. 
exhaust,  see  Exhaust, 
expansion,  see  Expansion, 
fly  wheel,  48-50,  123,  171-178,  249. 
gauge,  ills.,  16-18. 
gear,  see  Valve  gears, 
gibs,  127,  137-148. 
governor,  see  Governor, 
guide,  136,  229. 
gudgeon,  150. 
head  end,  90. 
high  speed,  96,  184. 
hoisting,  323. 
horizontal,  parts,  ills.,  48. 
horse  power,  see  Horse  power. 
Houston,  Stanwood  &  Gamble,  ills.,  57, 

126,  187. 
indicator  card,  see  Indicator  card, 
initial  pressure,  diag.,  64. 
lap,  see  Lap. 
lead,  see  Lead. 

Lidgerwood  hoisting,  ills.,  323. 
locomotive  cross  head,  ills.,  136. 
marine,  guides,  ills.,  133. 

valve  gear,  312,  313,  316,  319,  353. 
mean  effective  pressure,  68,  72,  73. 
Murray  Corliss,  parts,  ills.,  99. 
Newcomen,  37. 
non-condensing,  47. 


Steam  engine, — Continued 

operation,  47,  49. 

packing  ring,  ills.,  116. 

parts,  103-178. 

piston,  see  Piston. 

port,  see  Port. 

pressure,  expected  mean  effective,  76, 

pressure  plate  valve,  ills.,  302-306. 

Prony  brake,  ills.,  93. 

radial  gear,  ills.,  339-352. 

Ramsbottom's  rings,  ills.,  115. 

reciprocating  parts,  ills.,  50. 

regulator,  speed,  Gardner,  ills.,  385. 

reversing  gear,  see  Reversing  valve  gear. 

riding  cut  off,  see  Riding  cut  off. 

rods,  open  and  crossed,  ills.,  322,  325. 

rope  brake,  ills.,  95. 

rotating  parts,  ills.,  50. 

"rotative,"  49. 

running,  over  and  under,  131. 

Scotch  yoke,  def.,  155,  156. 

shaft,  see  Shaft. 

speed,  control,  385,  399,  401. 
regulator,  ills.,  385, 

stationary,  parts,  ills.,  50. 
shaft,  ills.,  157. 

steam  chest,  ills.,  181. 

stuffing  box,  def.,  109. 

tangential  velocity,  174. 

throttling,  243. 

valve  gear,  see  Valve  gear. 

variable  cut  off,  243-290. 
Stem,  valve,  see  Valve  stem. 
Stephenson's  link  motion,  ills.,  317-320. 
Strap,  eccentric,  226,  229,  234-236,  239-342. 
Stroke,  choice  of,  98. 
Stuffing  box,  109-111. 
Sturtevant  connecting  rod,  ills.,  150. 
Superheated  steam,  24,  45,  46. 
Sweet  pressure  plate  valve,  ills.,  303,  304. 
Swing  center,  offsetting  object,  251. 
Swinging  eccentric,  offset,  ills.,  250,  251 

variable  cut  off,  principle,  248. 
Syphon,  operation,  ills.,  3. 


Tangent,  152. 
Tangential,  speed,  154. 

velocity,  174.  ■ 
Taper  flange  bolt,  crank  shaft,  ills.,  164. 
Temperature,  def.,  5. 

absolute,  21. 

fusion,  27. 

scales,  ills.,  19,  20. 
Terminal  pressure,  62,  65,  66,  67. 
Theoretical,  card,  steam  engine,  61,  62,  74. 

mean,  effective  pressure,  69,  76. 
forward  pressure,  68. 
Thermal  unit,  British,  def.,  8. 
Throttle  valve,  ills.,  57,  99,  383. 
Throttling  engine,  def,  243. 

governors,  381-388. 

Gardner,  ills,,  384. 


INDEX  OF  GUIDE  No.  1 


IX 


Throttling  engrine,  governors, — Continued 

Hoosier,  ills.,  382. 

Judsen,  parts,  ills.,  380. 

Pickering,  ills.,  382. 

regulating  mechanism,  ills.,  388. 

Sinker-Davis,  ills.,  382. 
Throw,  eccentric,  236,  245. 
Tram,  ills.,  434. 
Travel,  valve,  204-205. 

.  half,  ills.,  202. 
Triple  expansion  marine  engine,  Raabe,  316. 
Troy  steam  engine,  ills.,  96. 
Turning,  effect,  steam  engine,  173. 

force,  152,  153. 
Twin  City  Corliss,  parts,  132,  148. 


U 


Unit,  heat,  8,  10. 
power,  12. 

thermal,  British,  def.,  8. 
work,  10,  78. 


Valve (s),  51,  179. 

admission^  195,  196. 

double  ported.  Reeves,  ills.,  299. 

maximum,  Allen,  ills.,  209. 

position,  ills,  197. 
Allen,  ills.,  208,  294. 
angular  advance,  ills.,  441-445. 
Armington  and  Sims,  principles,  295. 
auxiliary,  pump,  ills.,  413. 

Houston,  Stanwood  &  Gamble,  188. 

Richardson,  ills.,  291. 
Ball,  ills.,  307. 
Bilgram  diagram,  ills.,  213. 
bonnet,  ills.,  99. 
battens,  ills.,  448-450. 
Brownell,  ills.,  185. 
chest,  ills.,  105. 
constant  lead,  193. 
cut  off,  see  Cut  off. 
defects,  ills.,  218-224. 
design,  210-217. 
dimensions,  211-217,  448,  450. 
doublet  admission,  def.,  295. 

ported,  ills.,  295,  300,  301. 
early  cut  off,  207. 
edge,  steam,  ills.,  262,  265. 
equal  lead,  194. 
exhaust,  see  Exhaust, 
face,  length,  214. 
gear,  225-242. 

Allen,  335. 

Bremme,  des.t  ills.,  352-355. 
marine  engine,  ills.,  353. 
Meyer,  ills.,  279,  282. 
Rider,  ills.,  259. 

Gonzenbach,  259. 

Hackworth,  ills.,  340-348. 


ValveCs),  gear, — Continued 

independent  cut  off,  260. 

indirect,  232,  233. 

Joy,  ills.,  355-359. 

Lentz,  engine,  ills.,  251. 

link  motions,  ills.,  317-338. 

marine  engine,  Bremme  gear,  353. 
reversing  eccentric,  312,  313. 
single  cylinder,  ills.,  319. 
triple  expan.,  Raabe,  ills.,  316. 

Marshall,  348-353. 

parts,  225. 

poppet  valve  engine,  ills.,  251. 

pump,  see  Pump  valve  gears. 

reversing,  see  Reversing  valve  gears. 
Giddings,  ills.,  301. 
Gonzenbach,  ills.,  257-261. 
inside,  admission,  setting   ills.,  444-446. 

lap,  189-191. 
lap,  see  Lap. 
laths,  ills  ,  448-450. 
laying  out,  ills.,  214-217. 
location,  ills.,  50,  104. 
main,  ills.,  262,  265,  266,  268,  269,270. 
maximum,  eccentricity,  ills.,  203. 
modified,  291-308. 
over  travel,  def.,  205,  206. 
parts,  ills.,  180-186. 
passage,  supplementary,  209. 
Phoenix,  ills.,  191. 
piston,  293. 

balanced,  ills.,  296. 

double,  admission,  illr.,  294. 
ported,  ills.,  295. 

inside  admission,^  setting,  445. 
locomotive,  ills.,  296. 

Reeves,  ills.,  298. 

setting,  444,  446. 

Vauclain,  ills.,  296. 
port,  see  Port. 
positions,  admission,  ills.,  195-197,  215. 

compression,  ills.,  200,  201. 

cut  off,  see  Cut  off. 

during  one  stroke,  ill  .,  52,  53. 

exhaust,  180,  188,  193,  216,  301. 

extreme,  202,  203,  204,  215,  216, 
265,  280. 

late  cut  off,  ills.,  289. 

lead,  ills.,  192-194,  208. 

line  and  line,  ills.,  190,  191. 

mid-admission,  ills.,  289. 

negative,  lead,  192,  193. 
positive  and  negative  lead,  ills.,  436. 
pre-admission,  194,  195. 
pre-release,  198,  200. 
pressure  plate,  302-308. 
pump,  403-432. 
release,  199,  200. 
requirements,  179. 
seat,  180-183. 

battens,  448-450.  ^ 

dimensions,  recording,  448—450. 

formula,  216.  _  • 

length,  balancing,  183. 

limit,  215. 

neutral  position,  216. 


X 


INDEX  OF  GUIDE  No.  1 


Valve(s) , — Continued 

setting,  ills.,  433-462. 

emergency  rules,  446-447. 

pump,  404,  407,  409,  412,  421,  423, 

425    427. 
with  indicator,  des.,  ills.,  460-462. 
size  required,  various  cut  offs,  ills.,  222. 
steam,  edge,  ills.,  182,  262,  265. 

port,  tee  Port. 
stem,  104,  105,  226. 

connection,  227,  228,  230,  231,  234. 
templates,  ills.,  426. 
travel,  180,  202,  204,  205. 
variable  lead,  194. 
zero  cut  off,  288. 
Vaporization,  23,  28. 
Variable  cut  off,  243-290. 
independent,  253. 
offset  swinging  eccentric,  251. 
regulating  mechanism,  389. 
riding  valve,  methods,  263. 
shifting  eccentric,  246-248. 
swing  center,  offsetting,  251. 
swinging  eccentric,  248-251. 

offset,  251. 
Gonzenbach,  257-262. 
Vauclain  piston  valve,  ills.,  296. 
Vilter,  rope  wheel,  ills.,  178. 

types,  ills.,  173. 
Vim  direct  valve  gear,  ills.,  233. 


W 


Walschaerts  gear,  ills.,  360-362. 

Warren  pump,  valve  gear,  setting,  ills.,  427. 


Water,  absolute  zero,  35. 

boiling  point,  2,  28,  34. 

properties,  1,  2,  3,  4,  12,  27,  28. 

re-evaporation,  35. 

static  head,  meaning,  4. 

temperature,  12,  27,  28,  34,  35. 

U.  S.  gallon,  weight,  4. 

vaporization,  temperature,  28. 
Waters  throttling  governor,  reg.  mech.,  388. 
Watertown  engine,  crank  shaft,  ills.,  162. 
Watt,  James,  engine,  37. 
Wedges,  to  measure  lead,  ills.,  436. 
Weight,  atomic,  1. 

Westinghouse  connecting  rod,  ills.,  150. 
Wet  steam,  def.,  24. 
Whitney  hot  wire  instrument,  ills.,  7. 
Williams  link,  des.,  ills.,  317. 
Wire  drawing,  183. 

Woodbury  pressure  plate  valve,  ills.,  305. 
Work,  units,  8,  9,  10,  25,  78,  153. 
Worthington  duplex  pump,  ills.,  418. 
Wrist  pin,  compression,  ills.,  130. 

various,  127,  128,  129,  130,  145. 


Yoke,  valve  gear,  225,  226,  227. 


Y 

525,  22 

Z 


Zero,  absolute,  def.,  21,  35. 
over  travel,  ills.,  276. 


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